This is being discussed on a home builder forum that I follow as well. Some over there claim to know more details or know the pilot. Several points that were brought up was that it was the pilots home airport where he maintains a aerobatic box with a ground level waiver and it was in effect at the time, and it was a practice routine for this years air show season, the airport manager was briefed before hand, and the camera was on a tripod so he was further away from the second person than it looked.
I wasn't there so don't shoot the messenger, but I for one, hope this is true and there was a method to the madness.
If it is a practice routine, then there probably wasn't much more danger to the people on the ground than pole holders for ribbon cuts.