That guy's mouth moves a whole lot. A lot more than necessary. I imagine the director was like "Come on, people aren't going to believe you're really singing unless you move your mouth more," and the guy went wild. It's like his mouth is on crack or something.
His whole head moves. I've never seen someone's mouth and whole head move that much just singing. He has to open his mouth as wide as possible and swing his jaw side to side and do that thing with his neck. I can't stop laughing.