Baldwin is also the producer — responsible for vetting the people he hires — and he has probably worked on set with firearms enough times that he should know basic safety like checking the weapon before use.
There were like 11 “Producers”. There was an Executive Producer who ran things. Baldwin had nothing to do with management.
There were apparently crew members using the cool replica to shoot cans or whatever and that is probably how live ammunition got involved. The “armorer” did not hand the weapon to Baldwin. Of course, armorer was only part of her job. She was also a costume assistant. There seemed to be sloppy handling of fire arms and ammunition, which was her and others fault.
Baldwin was not the only one who messed up. However, it seems likely he pointed and fired the gun at the victim as a joke or threat, assuming it was not loaded.