You're still being dishonest. If someone pays you to work 9-5 and you don't work those hours you're being dishonest and in breach of contract. It's especially true since he goes out of his way to pretend he's working by playing a black screen video to keep his computer on.
He can try to negotiate something based on output, but what he's doing is a dick move
He can try to negotiate something based on output, but what he's doing is a dick move