He got on the trigger quick because he wanted to shoot quick. His holster magnified the error because it requires the trigger finger to apply pressure to unlock the pistol.
Everybody SAYS they follow the 4 safety rules, but most shooters don't. Honestly, they really don't. They fail to handle guns purposefully and they often make excuses for the bad gun handling they get called on.
Right, and it was bad gun handling that caused this ND. Nothing to do with the holster. If he trained correctly with the Serpa, then this wouldn't have happened. He shouldn't have been swapping around holsters and weapons and then attempting to run full speed drills.