I'm conflicted on this one for a number of reasons.
I do not like the shot after the guy was starting to back off. Had it been a split second after the shooter went down, I might have another opinion, but it sure looked to me like the aggressor was starting to back away after the gun came out. That to me would be the time to keep the gun up in a defensive position. However I wasn't there, and I'm not going to make a call based on the camera position of a blurry video.
That said, the aggressor pushed HARD. There didn't appear to be any "Hey, back off!" notice. He just saw a guy who was smaller/weaker than him and attacked. It was a pure bully move, IMO. I would be more inclined to think otherwise had I seen him rushing out the door and running straight for the other guy. That might have indicated he feared for his girlfriend's safety. But he didn't. He walked out in an almost nonchalant manner, and when he got within arms reach, he attacked. Sorry, but that to me is a bully move.
As far as overly avoiding situations, I guess I generally do when I'm packing because it seems prudent to do so in our current society with current views on self-defense and guns. I'm likely to be more of a loudmouth without the gun. That is, likely to be. I generally try my best to mind my own beezwax on everyday annoyances, armed or not, but would be more likely to be a buttinski without a gun on my hip. This does not include butting into situations where it looks like someone is in trouble. I've not run into that kind of situation, but if I did, I hope wearing a gun will not cause me to hesitate to act for fear of legal reprisals (even if the gun never leaves the holster).
Wherein the problem lies. "An Armed Society is a Polite Society". If we were to really live by that, the bully would have never made a shove to the ground his first response. Perhaps the guy who was shoved would not have approached the woman, or would have approached her in a different way. In an armed and polite society, only a moron physically attacks someone the way the guy in the video did if the someone is possibly carrying some variant of Sam Colt's equalizer. I will bet real money the shover never for a second considered that his victim might be armed. He fully thought he had the upper hand.
In many ways, to go on a tangent, this is why we have all the Internet / social media vitriol. A bunch of people who think they can do what they want with no repercussions, because they're safe behind their keyboards. They say things they would never say when their nose is within reach of someone's fist. Just like we have people that will make a physical response their first response, especially against someone who looks weaker, because they don't think they have a need to be polite, because it's not ingrained into them to think, "armed society - be polite".