? What are you talking about? You're not explaining anything. The sled is going down the track by itself. He sure as hell isn't steering it sliding on his butt.
And what's you're "explanation" for the first clip? I think the problem is you can't articulate your point clearly.
1. The sled is not going down the track by itself. The sled is going down the track connected to the person, who is splayed out and holding onto it, creating tons of friction which is slowing everything down. There is maybe 1 second in that clip during which the sled is actually sliding completely by itself. It goes about 5 feet before he grabs it again, controls it, and then climbs back on.
And what would you think would happen if he let go? That it would magically stop on the track?
Oh even this: aside from the difference of water & ice, structure & physics-wise how would a luge track be different from a waterslide?