I do like that ^ answer, but given the lack of wake or disturbance in the water ahead of it and the angle of plane that it's on, I
suspect that it's more likely a small, direct drive motor pushing it along; probably something in that dark mass which is just visible under the seat.
Back in my youth/ancient history, we used to make up all sorts of things like that for the various local ski shows - chairs on skis or surfboards that'd do impossible things; kids ride-on toy cars on skimmer boards that'd suddenly overtake the ski-boat that, until then, had apparently been towing them, and then it'd run rings around the boat or play 'chasey' as the boat tried to get the kids toy back onto the end of the tow rope; 'high-speed' paddle boards that'd seemingly move without the person on them
actually doing any paddling - all novelty stuff to keep the viewing public entertained. But they hadta actually
BE THERE to watch/see all of this fantastic stuff, none of this staying at home and watching it on a small screen waaay back then!