Untrue. They were out plinking WITH THAT GUN the previous night.
They left a round in the cylinder. Real life: they fucked up and that was the second link in the chain. First link: gun should never have left the armorer's custody. Third link: she was responsible for verifying the state of the gun before declaring "cold gun." Baldwin's behavior is the fourth link.
And by behavior I mean by running the production with unreliable, cheap labor.
There was a crew member in charge of arms on the set. Baldwin hired her. She failed at her job.
The assistant director failed as well, and he was the one who handed Baldwin the gun and announced "cold gun" to the set.
I used to do cowboy action shooting and they had stringent safety procedures. All competitors waiting to shoot had to have all firearms EMPTY, revolvers holstered and long guns with actions open. When your turn comes, you go to a loading table and load the guns under the watchful eye of at least one range officer. Then, after shooting the course you go to an unloading table where you demonstrate that all guns are unloaded under the watchful eye of at least one range officer. Minor infractions are punished by disqualification from a round and major infractions are punished by disqualification from the entire match.
I don't know if they still use the old 5-in-1 blanks that were standard fare in Hollywood, but those were red and had a distinctive bottle nose shape making them easy to tell apart from real ammo. As I said before, this particular set was having lots of safety and crew issues so perhaps the shooting was the natural result of a poorly supervised dangerous workplace.