His knees are up because he cannot lower himself full extended with his legs straight. that is pretty obvious when you see him standing before he even grabs the bar. Those things do not work if you are normal height.
Sorry, but you're wrong. His knees shouldn't be up at all. If he kept his hips straight but just bent his knees so that his feet would be behind him, then he would be doing it right. But he's too weak to do it without some sway (momentum), so he raises his knees to get some, and can't even do a decent range of motion, let alone full range. Bottom line: He doesn't know what he's doing and/or he doesn't have the strength to do it -- but the bar "works."