It's not necessarily a threat of violence. A lot of people would just feel ashamed to criticise other people in person would feel fine to do it on the Internet. Being a dick is a lot harder when you can see the effects of your words on the other person.
Yeah but that doesn't mean the guy was trying to be a dick either. Someone could say something to me with good intentions and they can't help it if it pisses me off.
Tbf, a threat of violence is only one way to read his response (I know nothing about this Paul dude and his personality, so maybe it was 100% a threat idk).
I could also see his comment as meaning "just because you're behind a computer screen doesn't mean you should feel able to say shit that you'd never say to a person's face", because let's be honest, that's a reminder a lot of folks on the internet could use, regardless of who could kick whose ass