Serious question, would it have been legal for these people to shoot him in the state where he was?

Depends, and it depends on the jury. "Stand Your Ground" laws essentially make it legal to shoot somebody if you believe yourself to be in mortal danger, where the usual standard is that you can use violence to protect yourself as a last resort, but not if there are any other options available. I suppose if you were able to convince a jury that you believed that this joker was a real-deal threat to your life, maybe. But good luck with that. In states that do not have a "Stand Your Ground" statute, almost certainly not. But the law can get weird, and Americans love guns and are often friendly to self-defense defenses, no matter how flimsy. But, on balance? Probably not, no.

What I'd like to know is whether you can tell people not to touch your vehicle and whether you could be arrested for doing it if they've told you not to. I have no idea about that.

Oh, and this guy is gonna get hurt.