I used to ride a honda XR650 in the desert, it sucked. Too much bike to muscle around. The I'd get on a 125 and scream all over. it was super easy to ride instead of ride-along.
This guy is on a bike that is "flickable." That makes all difference in the world in tight conditions. He can redirect the bike MUCH faster than someone on a "bulkier" bike. I think on a 14/12 bike he would have gone even faster!