This is not how it happened.
Joe shoves the guy out the way from the back instead of saying "hey excuse me" like a normal person.
The drunk guy probably felt some way and said something like a normal person. "Hey man you could've said excuse me."
Joe turns around, says something, the guy attempts to walk forward to probably get into Joe's face to confront him about whatever Joe said and and Joe hits the dude. The camera is completely blocked from what the guy did but still even if the guy was a threat who rushes a threat? You're supposed to get distance between a you and a threat. So the fact Joe felt comfortable enough to get in that guy's face throws away any "he was a threat" argument. If that guy was Ngannou, Jiri, Overeem, Stipe, Whittaker, etc Joe Shilling is getting distance from them not getting in their face because they are real threats. Joe in this situation did the shit because he felt he could not because the guy was a threat.
Whoever says the guy was throwing a punch at Joe is lying. At the worst you can say the guy was attempting a headbutt because his head is the only thing that came forward.