Well that's an incredibly narrow minded view of responsibility and fault, but whatever. I think it can not be your fault if there's a system in place that you're meant to rely on, and that you're told by people who are supposed to know better than you that it's not dangerous and it's ready for the scene. He's just an actor, it's not his job to be a prop or weapons expert, he relies on other people who are supposed to know more about it than him. A film set, much like many other workplaces, relies on different people contributing in different ways, for the purpose of efficiency, that's all he did. He did the same thing he's probably done many times, and the reason it went different this time is because someone else failed in their responsibility. If a mechanic of a race car fucks up and it leads to an accident where someone in another car gets killed or injured, is it the driver's fault for trusting the system they've always relied on?
And yes, I do think he could have trauma.