Did the guy have the right to be there? Yes.
Could the OP determine he was a gang banger? Yes, having been around many gang bangers myself, I know that one can intelligently estimate whether someone is a gang banger or not. The OP failed to use his politically correct keyboard when making the post. Personally, I view that as a good thing. Political correctness is destroying this nation. If the OP said he was probably a gang banger; that is good enough for me. I will take it at face value.
Other than being a fool with his ammo, the guy was not being dangerous. His bullets were travelling in the right direction; they just rarely hit their target. I probably would have sat back, pretended that I was working on a firearm and watched the guy waste his money. And when he was done, I’d go back to shooting. That way I would be safer than I would be standing next to him. And, if I saw him getting dangerous, I could leave without embarrassing the gang banger in front of his woman.