It's still not definitively confirmed that the guy was a right winger, his family might have been MAGA but the guy himself could have very possibly been radicalized recently by the endless ragebait "anti-fascist" posts and did the deed as a result. It would explain the casings at the very least.
From what I've seen, the entire assumption that the guy was a rightoid comes from the fact that his family is MAGA and that's pretty much it.