re: Tetrahedron
If it landed on a point, it would tend to fall over. Suppose base was the flat side opposite the point. Then it would end up on it's side. But as it opened up at the point, those three sides hinged on the flat side edges, unfolding, would cause it to further roll onto the flat side. That's the worst case scenario, but if it is bottom heavy, it may have simply rolled correctly onto its base.
