No, it wasn't one case, but an outbreak. That appears to have been a misinterpretation of the claim.
Fortune put the outbreak at 'about 150' COVID-19 cases.
The size of the disruption to supply chains is backed by a media briefing from shipping company Maersk
Seatrade Maritime News reported on the claim:
Putting the magnitude of the issue at Yantian port is causing container shipping into sharp perspective Vincent Clerc, AP Moller-Maersk’s CEO of Ocean & Logistics, stated: “I would say this for us is a much bigger disruption than the Ever Given getting stuck in the Suez Canal for some days because of the duration and the importance of Yantian as a gateway.”
The blockage of the Suez Canal only lasted for six days, while the situation in Yantian has already lasted several weeks with no end in sight for the coming weeks either. The port handles around 13.5m teu a year or about 36,400 teu a day, making a key gateway port on a global scale.
“Right now, we have vessel delays of up to 16 days outside Yantian which is of course going to cause significant ripple effect across the network from a reliability perspective,” Clerc explained.
Lars Jensen, CEO of Danish consultancy Vespucci Maritime, made similar claims:
Yantian handled 13.3m teu in 2020, equal to 36,400 teu per day. Presuming that Yantian – responsible for more than one-third of Guangdong’s foreign trade and one-fourth of China’s trade with the US – has been working at 30% operating efficiency since the Covid-19 outbreak was detected 14 days ago, that would mean 25,500 teu per day have not been handled, totalling some 357,000 teu to date.
Putting this in context, when Suez was blocked by the Ever Given this impacted a daily flow of 55,000 teu. However, March’s Suez crisis lasted for just six days.
These seem to be back of the envelope calculations performed by experts who have a financial stake in the outcome, rather than a full peer-reviewed analysis by economists, but it appears reasonable justification for the journalist using it as a comparison to help people understand the magnitude of the problem.