Civil lawsuits are common in even the cleanest cut and dry self-defense shoots. Pretty fucking pathetic IMO. Hopefully his homeowners or rental insurance will cover a decent attorney for him.
May I suggest a personally liability umbrella. It requires you to max out the liability limits on your homeowners and auto insurance policies and they are pretty cheap considering. A $4 million personal umbrella costs me $350/yr through State Farm and its billed along with your auto insurance.