Not sure why you're so hung up on what he said. He could easily show in court that during production of a film, it is not customary for the actor themselves to check and deem a weapon safe and that the responsibility falls on the armorer. Her question and his comment are meaningless in this. Just because she asked if he'd like to check doesn't then transfer liability to him.
It would be like Joe Q. Public taking his car to Discount Tire for repair work, then afterwards gets on the interstate and an improperly torqued wheel goes flying off into a bus full of nuns, killing them in the process. It wouldn't make two shits if the Discount Tire tech asked the customer before he pulled off "hey, you wanna check the torque specs on those lugnuts?". The onus doesn't then fall to the customer just because the trained professional asked if the untrained person would like to verify. That's not their job.