I am completely unfamiliar with gun laws, and your comment about discharging firearms in the city limits got me curious enough to look up the city codes. 

Various codes about firearms are sprinkled in various places, so it's entirely possible that I missed one, but I can't find the law prohibiting discharging a firearm in your own home within the city limits.

I've found code 4.885, which prohibits (with the obvious exceptions) discharging firearms, but that appears to apply only to the Downtown Public Safety Zone. I've also found park rules (which I believe carry the force of law) against discharging firearms in city parks and open spaces.

I very likely missed something, but right now I'm not so sure he broke the law when he shot his floor.