He didn’t ignore basic gun safety. Firearms on movie sets are not the same as firearms everywhere else. There is supposed to be a dedicated person who is directly responsible for ensuring live ammunition is never, ever brought close to a prop gun. I’ve posted this elsewhere at one point, but as somebody who has worked on productions with blank-firing guns, the cast and crew are not allowed to inspect, touch, or come near any firearm on set apart from the shortest time required for the scene. The firearms are secured before and after the scene, and there should never, ever be a chance for live ammunition to get inside a prop. The armorer guarantees the gun is safe, and are the ones responsible for it.

The armorer for this production appears to not have followed those protocols, and that’s where Baldwin’s potential culpability is-- not as an actor who shot somebody, but as a producer who should have had better oversight of the armorer.