Oh, no!
Not an assault pistol! Those things can be dangerous.
That said, how was he stupid enough to get caught?
New Jersey used to send tax agents over to shopping centers in Pennsylvania. They’d record the license numbers of cars with NJ plates. I suspect Kalifornia has a rat/s that check Nevada FFL dealer’s parking lots. It wouldn’t be hard to mosey in when a Kalifornia tagged car is parked outside. Customer buys a banned item, he’s screwed. Cops pick him up on the way in.