The way it reads, I'd have to seriously consider charging him. If I'm reading it correctly he fired a shotgun into a door without knowing who or what was on the other side.
Options other than shooting blindly into a door:
1) Pound on the door and yell that the police have been called.
2) Bust the door open and go in yourself if you're so sure you're right. (Yes, I know it's not as easy as TV and movies make it look, but it's also not that hard)
I'm as much of a gun guy as anyone, but that doesn't mean a gun is always the correct tool.
Fortunately everyone came out ok, and I suspect he won't be charged because he was lucky enough to be right. What happens when some guy shoots a door open only to find out his neighbors were just engaging in some loud rough sex?