Two lessons here:
1- anyone who is that fearful shouldn't be carrying a firearm. I'm a big proponent of 2A, but this is ridiculous - if the man is that big of a 'pansy' that he's in fear for his life because someone shoved him (and wasn't even continuing to attack him), he's no man.
2- don't put your hands on someone without expecting retaliation. There are 'pansies' like I mentioned above as well as unstable people - neither of those are going to respond normally to getting shoved, grabbed, etc. The 'pansy' night have been yelling at the guy's girlfriend, but nothing about his body language was threatening, so shoving him was unnecessary escalation.
The shooter should not have shot the guy from what I can see, but I also cannot see anything that makes me think the boyfriend had any reason to lay his hands on the man.
Such an easily avoidable situation...