It's not powered. It's just like having half a wagon hooked to a post and instead of them being out in front of the wheels, they're between them. They pull it around. The seat can be moved to the opposite end too, so the horse can be hitched in there to go around either way. The way it's set up now, you'd be going around counter clockwise.
Yeah - I'd be interested to see either pics or a movie!
I hadn't noticed that rider was completely without stirrups. Those guys are pretty good riders, eh?