That's irrelevant though, you can only judge offside from the point that Stones heads the ball, and the contact by Silva on Sa happened before that. If Silva was to be penalised for anything it could only be a foul, and it was nowhere near enough contact to make it that.
The issue here is that Tom Bramall flagged it as offside, can understand why as from his angle it may have looked like Silva was blocking Sa's view. Replays show he clearly wasn't, and had the flag not gone up I don't think there would have been a review at all, Attwell would have quickly cleared it. But they obviously felt that as it was given as offside on field it needed to pitch side review