I just saw another interview. He pulled the hammer back and released it. Appears it wasn't far enough back to cock but still far enough to fire when released.
I guess that's technically possible. But all the single action revolvers of that type that I've ever dealt with had a half cock position that you have to use to even load the weapon. It's hard for me to believe that either: half cock didn't catch the hammer or that the hammer had enough inertia to ignite the primer before the half cock position. Anyhow, all the info will come out eventually