The answer, as any American man and most women can tell you, is that every gun is hot, and you never aim one at anyone else, ever. And you never pull the trigger, ever. Never trust someone else to have cleared the breech and emptied the mag. The gun is always the full responsibility of the person holding it.
Unless you are an actor performing a scene, which he was not doing at the time.
He did what he would have claimed all crazy redneck gun owners do... he clowned around with a gun, pointed it at others, and pulled the trigger.
And now his inner asshole, never far from the surface, is coming out.
It IS starting to sound like it was real ammo with bullets. That is incredibly stupid for a movie production. Some else has a share of this blame.
But Baldwin is a grown man, an American man, a man who ought to know better than to point and click for fun.
My wild-guess supposition now is, his asshole self was trying to frighten the woman, for fun.