If you watch it, he is cutting the power at the very top of the loop to get the nose to "swing" (for a lack of a better word) down faster and then as soon as it does so, he is going to full power to finish the loop with.
I use this trick for my RC flying when doing loops close to the ground (just like he was). now not knowing much about ultra-lights, it also might be for other reasons such as not overspeeding it and ripping it apart (that is a complete guess, i dont even know how fast the dam things can go).
Ah, now I see what your saying.
When I do aerobatics I don't cut the power, but I don't fly ultra-lights either. I think his loops would be a lot more rounded if he'd use the power, because right now it looks like like an egg. I'm not saying that he's a bad pilot, it's just not the best way to make a good loop.
