More accurately, of course, someone who has control of the domain COVID.gov has changed its content (or where it points to).

Here's what it was last week:

https://web.archive.org/web/20250410231214/https://www.covid...

"Seized" covid.gov when they already controlled it? lol

"The White House put up a POSTER!!!" https://m.xkcd.com/932/

As you said, the difference is that they already control it: it's not some hackers defacing a government website for lulz, the defacement is coming from inside the government.