I agree and I don't think he's the type but it wouldn't surprise me if he wasn't as focused as usual and that showed in his performance. I bet the Arsenal board wouldn't be at all disappointed if he did though. It'd give them some wriggle room to placate their fans.
He won't start. He'll likely get 15mins or so at the end of the game, so it might be hard to read too much into it.
And I agree with Karen, whether he plays or not has no indication whether he stays or goes.