It's all a bit up in the air really. In this instance, the batsman is out stumped, as he wasn't trying to run, so it doesn't matter whether he hit it or not, as the Keeper took the bails off. The stupid thing is, that if the batsman defends it to silly point say, who then hits the stumps, he is run out, rather than stumped, as although he's not attempting a run, a fielder can not perform a stumping, which is stupid because it should be stumped in my view.