He's an awful footballer as in he cannot kick it to save his life, his technique is appalling, his passing is disgustingly bad and he panics in possession, that's what I mean by he's an awful footballer. I'd wager if it was me versus him in a game of crossbar challenge I'd win because he's that bad at the basic idea of kicking a football. I am utterly shite though.
What he is though, is an athlete that can get himself out of situations by being really, really quick. If you're quicker than your opponents then you've got a much better chance to get to the ball before them and therefore not look quite so bad at the game as you actually are. If you've got a knack for spotting danger too which I suppose he does then you can be a decent defender.
Not many central defenders are actually good footballers, same with goalkeepers. They don't have to be as long as they can get something in the way to stop an attacker.