For practical purposes, his act of "brandishing" probably saved him quite a bit of trouble. If that area is known to have a lot of criminal ativity, I probably would have done the same.
From a legal standpoint (Florida's Laws), That would be considered a misdemeanor. There is an obligation to retreat if possible to avoid using lethal force if you can do so safely (unless you are in your own home).
If you warned someone to stay away and they still approached agressively, I think most of you would do the same thing.
The ATF should be a convenience store instead of a government agency!