In the video he does run on tiled stones even and over a small gap, see 0:39 to 0:49. It looks like he's not struggling but it's such a closeup that you cannot see if he lost balance or not afterwards. I'm still very skeptical though, that gap would be quite hard to cross on a skateboard without a small jump and on a skateboard your center of gravity is almost 2 feet further back than on this thing. Maybe the propulsion in the wheels help.