However I won't be at all surprised if it turns out that the aircraft had been hired and the pilot was volunteering -- flying for fun, as at any gliding club with a tug or at a jump club. Perfectly legal.
To carry out these activities one has to be member of the gliding club or para club that is being operated for. I suppose this could be the case for wingly flights (i.e. set up a club). Wingly is just nuts. If I hire a car and a driver he has to meet higher standards than if I self hire.