I think he probably had enough gun, alright. The mistake? I'd guess he shot at "the brisket". Moose are a big target and a hunter who gets a tad glassy-eyed will just shoot at it or shoot at the shoulder - or the brisket. Nope. Shoot at the heart when they're face on. This has always been true: "Aim small, miss small."
Second, he fired one shot and left to walk up on it. Nope. You get another load up the pipe and stand there. Wait 2-3 minutes at least. If it gets up, put another one into it right now. Too many times a hunter will shoot once and then wait for an animal to drop/die. That's not a good idea, specially with moose.
Awesome video, tho.
I'd hunt with him in a minute. He seems like a slightly crazy sob who is not full of himself and not afraid. There'd be stories to tell for sure.