I used to love sliding down stairs… not as a baby, but when I was a little kid. This kid has his technique down pat, but if I were him, I’d flip over on to my but. I can’t see that being a good idea for the kid’s future in reproduction.
This should go without saying, parents don’t try this at home. Just because this kid is awesome doesn’t mean yours is a special little snow flake. And… if a stunt like this were to go bad, your kid could end up a whole different kind of special.