Yes, but if you don't bring to even half cock and the hammer slips out of thumb, cylinder reverses. There should never have been even blank in that aligned cylinder, much less a live round.
I despise Baldwin, but this is on the armorer.
I have a single action Italian reproduction Colt 1851 ( it has the half cock feature ). If I pull the hammer back and release it prematurely then the cylinder DOES NOT ROLL BACK. repeat: the cylinder DOES NOT ROLL BACK. I just tried it many times.
It sounds like a cascade of failures - a most catastrophes are.
Sure the armorer may be negligent, but Baldwin should have cleared the firearm. He said they were just lining up the angles for the scene or something and no trigger pulls were planned.