Actually, no. Murder is the deliberate killing of a person. If the person in your example believed the gun wouldn't go off, then it isn't murder. Negligent as hell, yes. Manslaughter, certainly. But not murder, because it doesn't meet the definition.
The entire point of the post is that it isn't credible that the person actually thought their killing machine couldn't kill: pointing a gun at someone with the intention of killing, and pulling the trigger, counts as murder, even if you thought the person would magically survive if they were innocent.
You're free to try to make a case otherwise, but it'll be an uphill battle against reason.
Not my fault, I was certain that they would move out of the way of the bullet.