While I agree with your thoughts on .22 LR, at least one person in the audience was killed. The threat was very real.
.22 LR is probably lib disinformation to minimize the seriousness of the attempt. Remember, 5.56 NATO is also a .22 bore and is a reasonable choice for a few hundred yords.
My preliminary wild guess is that this was an Antifa guy who took a 22LR rifle from his dad’s bedroom closet, and decided to change the course of history.
Eh, perhaps we will never know the real truth. And as others here have noted, how could the shooter be on a rooftop, and not be noticed by the Secret Service? It would seem to me that securing rooftops would be taught on the first day in the SS academy.