The problem with this statement is that prop/inert cartridges are labeled and identified as such in ways that are usually fairly obvious.
Like “loading” the cartridge with a steel ball bearing, and a used/fired primer cap (which has a divot from the hammer.) Thorough inspection would have identified them as inert.
While it’s remotely possible they were so well crafted as to be virtually identical, that kind of thing would end the props company. They are very careful to always make the marking conspicuous- as long as you know to look for it. (Another common option is a somewhat large hole in the side of the casing.)
And the indicators should have been gone over in a safety briefing so everyone knows. (And is trained in what to do on seeing a live round. “Hey! Live round! armorer!”)
In any case Baldwin had a duty of care to handle the firearm safely. Part of that includes knowing its state. He did not clear the fire arm, and did not know its state. It becomes self evident they were not inert cartridges but rather live rounds given that we’re talking about Alina being shot.