The black husband, who has just violently shoved the white man to the ground, doesn't back up until he sees the white man pull out a gun. This isn't surprising; the black man, according to his wife, was just trying to protect her. Men who are trying to protect their wives don't back up. They want to make sure that the problem is taken care of. He wasn't coming back in to beat on the white man he had downed--but neither was he retreating.
The question is: given what he had just done to the white man, does the white man have reason to believe that he is in mortal danger? Remember: the black man has blindsided the white man, shoving him to the pavement with extreme prejudice. If I'm that white man, I'm forced to wonder whether this particular black man has a gun on him.
I always ask myself if I would view this the same way if the races were reversed. Suppose it was a black man who was hovering around a white woman in a car, telling her that she'd parked illegally and asking her to relocate? Suppose that white woman had exited the car, as the black woman did here, and suppose at that precise moment, a large white man, her husband, had returned from his errand and straight-armed the black guy to the ground? If that black guy, fearing for his life, had taken out a gun and fired one shot into the white man, would I be defending the black man?
You're damned right I would.
So I'm defending the white man here. Regardless of the problematics of him playing parking-spot vigilante, he did NOT deserve to be shoved to the ground by the black husband. In Florida, that is at minimum basic battery, a first-class misdemeanor, and quite possibly felony battery. (Look it up. I looked it up.)
One takeaway here is that it's always a bad idea to lead with your fists, as the black guy did. Just a stupid thing to do.