I think he knows that the whole tent city is a fake. He may have seen them out of costume, when he was "taking tests". I bet the room Miss Clue was talking about is in the hatch. She asked Michael if Walt had ever been in places he shouln't have been. He may have been mentaly sending himself out to warn the Losties, and was caught and place in a room that could somehow stop him. Maybe thick lead walls white noise,or strong magnets. The thing that struck me as slightly odd was during this rushed meeting Walt asks about Vincent. It may be nothing but, a boys love of his dog. Then again maybe he knows Shannon who was looking after him was killed. He was there right before it happened. OR...? I don't know
I'm babbeling now.