His finger was on the trigger as he drew and pulled the hammer back. Very difficult for someone inexperienced with guns to not pull the trigger while doing this. Never put your finger inside the tigger guard until you have the gun pointed at something you intend shoot.
Correctimundo: While Baldy may think he didn’t “pull” the trigger, holding any pressure on it has the same effect. On that single action even light trigger pressure overrides the half-cock safety and eliminates the sear contact. So fanning the trigger means it’s gonna fire. Which is pretty much what the fedz said.