Why is it silly? Really no different to a hang glider launching from a hill top.
As a paraglider pilot, as well as jet & SEP pilot, I don't get it. I also have no idea how he arrived at takeoff. I have no idea why anyone would want to do it. The take off is gravity, no big deal. A hang-glider or paraglider takeoff is much more than that. A sailplane is easier. What the video purports to show skill in is the landing. So why not do a normal takeoff with engine, fly over this take off and switch it off. The dead-stick take off is not so smart. The reward/risk factor is......????