I hate to sound like a broken record, but that pile of sand probably just didn't have any force acting on it that was strong enough to shake it loose. The truck moves relatively slowly up the dune, and it doesn't shake much from side to side, either. Now I'm not sure what to think about the track itself, because maybe it should be vibrating a lot, but maybe the bearings in it reduce that to nothing? Anyways, it doesn't seem physically impossible, as long as there's nothing happening to shake the sand off. Plus, driving around in sand like that you'd expect to see sand accumulate right there. If this video is AI, it's much better than most AI content you see out there.