They may have not put out a press release (yet), but they said the same thing as to the Atlantic to other media organizations, some of which have included snippets from those communications e.g.:
The CDC's practice was first reported by Miami public radio station WLRN on Wednesday and was confirmed by the agency in a subsequent email to NPR. [...]
CDC spokeswoman Kristen Nordlund wrote in an email to NPR that the "majority of the data is PCR testing" but acknowledged that the agency's tally includes antibody testing because "some states are including serology data" in their testing numbers.
"Those numbers still give us an idea of the burden of COVID-19," Nordlund wrote.
She added, however: "We hope to have the testing data broken down between PCR and serology testing in the coming weeks as well."
CDC spokeswoman Kristen Nordlund described the agency's practice to CNN on Thursday and confirmed it the next day.
"Initially, when CDC launched its website and its laboratory test reporting, viral testing (tests for current infection) were far more commonly used nationwide than serology testing (tests for past infection)," she said in an email. "Now that serology testing is more widely available, CDC is working to differentiate those tests from the viral tests and will report this information, differentiated by test type, publicly on our COVID Data Tracker website in the coming weeks."
Also CNN has more details on which US states did that mixing
Contacted by CNN, public health officials in most states said they haven’t combined numbers from antibody and diagnostic tests. But 11 states reported mixing the numbers together at some point.
Colorado, Delaware, Georgia, Maine, Mississippi, Missouri, New Hampshire, Pennsylvania, Texas, Vermont and Virginia have all done so, but some states have stopped the practice.
Officials in Virginia and Vermont said they’ve fixed the issue. New Hampshire said it only reported the combined numbers for a day, and Colorado said it did so for about a week. Maine now separates out its numbers as well.
Texas said it will be separating the numbers this week, and Georgia says it’s working to provide greater transparency. Of the 50 states and the District of Columbia, CNN has not yet received responses from Alaska, Arizona, Florida, Iowa, and Kentucky.
(The Atlantic piece that prompted this question had some of those mentioned too, some backed up by links to the states' official statements.)