Mixon's response should have zero impact on whether or not Molitor's prior actions were grounds for an arrest. Saying that Molitor is also at fault does not mean that Mixon is not. I don't know Mixon, so I can't say he's a complete piece of . . . . , but punching Molitor the way he did was an absolute piece of . . . . move.
Outside of the legalities and just speaking from common sense, I think it's dumb to fight regardless of your size or gender. I was raised to only get physical if it was in self-defense and if it was an absolute last resort. Whether it's a big guy, big girl, small guy, small girl, etc., I would almost always flee before getting physical. I always thought I could hold my own in the event that someone ever attacked me, although weighing 80 pounds in high school would probably suggest that I would have gotten my ass handed to me, even by most high school girls. Actually instigating a physical altercation when you know you're at a massive disadvantage is just a terrible idea. What's happened in the aftermath of this incident is probably the best case scenario for doing so, which is to say, there's no upside. If alcohol were involved, which I'm guessing it was, it's even dumber.
At any rate, hitting her the way Mixon did was completely unnecessary and wrong. Trying to start a fight like Molitor did; pushing, slapping, and based on the grainy video, potentially grabbing Mixon by the throat, is also wrong, even if it's to a lesser degree on the wrong-ness scale.
Whether I have a son or a daughter, and regardless of whether they're physically strong or not, I would always advise them to treat people respectfully and do everything they can to avoid physical confrontations even if it means running from a fight. And I don't think that saying that hitting people is bad regardless of their size and gender would make me a poor parent.