guessing, and they have been for the past two months. They're still guessing now.
Now some guesses are much more accurate than others; in general, I would trust what Fauci says even after this statement. But he's not infallible, nor is anyone else in the medical/public health establishment. Or the Media, or the Democrat Party.
If Hillary Clinton were president this would be a non-issue and everyone would be chalking it up to Fauci acting on incomplete information. But since the Media have a Captain Ahab-like obsession with taking down the Bad Orange Man, we get all this silly Monday-Morning Quarterbacking and Gotcha! journalism.