The answer to this is going to opinion based to some extent. The WHO like everyone else was largely dependent on China for information at that point. Here's for example what the ECDC reported/concluded on Jan 17:
This info had to be counterbalanced against the clusters observed, from the ECDC report:
The WHO seems to have said something similar about the family clusters being a little troublesome, although seemingly just in a press conference, according to an answer on politics SE:
So it was a matter of balancing the overwhelmingly negative tests reported by China with the few epidemiological findings to the contrary. As that press conference suggests, not everyone inside the WHO was equally convinced of how to weigh these somewhat contrary findings coming from China.
So you can quibble about wording like "no significant" vs "limited" but it doesn't look like any major health authorities [outside China] could infer the magnitude of the problem at the time. Basically, the WHO, the ECDC and the US CDC were reading the same findings put out by China and coming to fairly similar conclusions in that Jan 14-17 time frame.
Very long aside below, but hopefully insightful as to what was going on in China in those crucial days:
China didn’t warn public of likely pandemic for 6 key days
In the six days after top Chinese officials secretly determined they likely were facing a pandemic from a new coronavirus, the city of Wuhan at the epicenter of the disease hosted a mass banquet for tens of thousands of people; millions began traveling through for Lunar New Year celebrations.
That delay from Jan. 14 to Jan. 20 was neither the first mistake made by Chinese officials at all levels in confronting the outbreak, nor the longest lag, as governments around the world have dragged their feet for weeks and even months in addressing the virus. [...]
It’s uncertain whether it was local officials who failed to report cases or national officials who failed to record them. It’s also not clear exactly what officials knew at the time in Wuhan, which only opened back up last week with restrictions after its quarantine. [...]
Without these internal reports, it took the first case outside China, in Thailand on Jan. 13, to galvanize leaders in Beijing into recognizing the possible pandemic before them. It was only then that they launched a nationwide plan to find cases — distributing CDC-sanctioned test kits, easing the criteria for confirming cases and ordering health officials to screen patients. They also instructed officials in Hubei province, where Wuhan is located, to begin temperature checks at transportation hubs and cut down on large public gatherings. And they did it all without telling the public.
The documents show that the head of China’s National Health Commission, Ma Xiaowei, laid out a grim assessment of the situation on Jan. 14 in a confidential teleconference with provincial health officials. A memo states that the teleconference was held to convey instructions on the coronavirus from President Xi Jinping, Premier Li Keqiang and Vice Premier Sun Chunlan, but does not specify what those instructions were.
“The epidemic situation is still severe and complex, the most severe challenge since SARS in 2003, and is likely to develop into a major public health event,” the memo cites Ma as saying.
The National Health Commission is the top medical agency in the country. In a faxed statement, the Commission said it had organized the teleconference because of the case reported in Thailand and the possibility of the virus spreading during New Year travel. It added that China had published information on the outbreak in an “open, transparent, responsible and timely manner,” in accordance with “important instructions” repeatedly issued by President Xi.
The documents come from an anonymous source in the medical field who did not want to be named for fear of retribution. The AP confirmed the contents with two other sources in public health familiar with the teleconference. Some of the memo’s contents also appeared in a public notice about the teleconference, stripped of key details and published in February.
Under a section titled “sober understanding of the situation,” the memo said that “clustered cases suggest that human-to-human transmission is possible.” It singled out the case in Thailand, saying that the situation had “changed significantly” because of the possible spread of the virus abroad.
“With the coming of the Spring Festival, many people will be traveling, and the risk of transmission and spread is high,” the memo continued. “All localities must prepare for and respond to a pandemic.”
In the memo, Ma demanded officials unite around Xi and made clear that political considerations and social stability were key priorities during the long lead-up to China’s two biggest political meetings of the year in March. While the documents do not spell out why Chinese leaders waited six days to make their concerns public, the meetings may be one reason.
The National Health Commission also distributed a 63-page set of instructions to provincial health officials, obtained by the AP. The instructions ordered health officials nationwide to identify suspected cases, hospitals to open fever clinics, and doctors and nurses to don protective gear. They were marked “internal” — “not to be spread on the internet,” “not to be publicly disclosed.”
In public, however, officials continued to downplay the threat, pointing to the 41 cases public at the time.
“We have reached the latest understanding that the risk of sustained human-to-human transmission is low,” Li Qun, the head of the China CDC’s emergency center, told Chinese state television on Jan. 15. That was the same day Li was appointed leader of a group preparing emergency plans for the level one response, a CDC notice shows.
[...]
“They may not have said the right thing, but they were doing the right thing,” said Ray Yip, the retired founding head of the U.S. Centers for Disease Control’s office in China. “On the 20th, they sounded the alarm for the whole country, which is not an unreasonable delay.”
If health officials raise the alarm prematurely, it can damage their credibility — “like crying wolf” —and cripple their ability to mobilize the public, said Benjamin Cowling, an epidemiologist at the University of Hong Kong.
[...]
[Earlier on, Chinese] officials obstructed medical staff who tried to report such cases. They set tight criteria for confirming cases, where patients not only had to test positive, but samples had to be sent to Beijing and sequenced. They required staff to report to supervisors before sending information higher, Chinese media reports show. And they punished doctors for warning about the disease.
As a result, no new cases were reported for almost two weeks from Jan. 5, even as officials gathered in Wuhan for Hubei province’s two biggest political meetings of the year, internal China CDC bulletins confirm.
During this period, teams of experts dispatched to Wuhan by Beijing said they failed to find clear signs of danger and human-to-human transmission. [...]
The second [Beijing] expert team, dispatched on Jan. 8, similarly failed to unearth any clear signs of human-to-human transmission. Yet during their stay, more than half a dozen doctors and nurses had already fallen ill with the virus, a retrospective China CDC study published in the New England Journal of Medicine would later show.
The teams looked for patients with severe pneumonia, missing those with milder symptoms. They also narrowed the search to those who had visited the seafood market — which was in retrospect a mistake, said Cowling, the Hong Kong epidemiologist, who flew to Beijing to review the cases in late January. [...]
“I always suspected it was human-to-human transmissible,” said Wang Guangfa, the leader of the second expert team, in a Mar. 15 post on Weibo, the Chinese social media platform. He fell ill with the virus soon after returning to Beijing on Jan. 16.
When the Thai case was reported, health authorities finally drew up an internal plan to systematically identify, isolate, test, and treat all cases of the new coronavirus nationwide.
Wuhan’s case count began to climb immediately — four on Jan. 17, then 17 the next day and 136 the day after. Across the country, dozens of cases began to surface, in some cases among patients who were infected earlier but had not yet been tested. In Zhejiang, for example, a man hospitalized on Jan. 4 was only isolated on Jan. 17 and confirmed positive on Jan. 21. Shenzhen, where Yuen had earlier found six people who tested positive, finally recorded its first confirmed case on Jan. 19.
The Wuhan Union Hospital, one of the city’s best, held an emergency meeting on Jan. 18, instructing staff to adopt stringent isolation — still before Xi’s public warning. A health expert told AP that on Jan. 19, she toured a hospital built after the SARS outbreak, where medical workers had furiously prepared an entire building with hundreds of beds for pneumonia patients.
“Everybody in the country in the infectious disease field knew something was going on,” she said, declining to be named to avoid disrupting sensitive government consultations. “They were anticipating it.”
So yeah, as the WHO (and US CDC, ECDC) was/were repeating what China had said a few days prior, the Chinese authorities were themselves waking up to the true extent of the problem and gearing up the response... while not quite revealing it in public until the 20th or so.
