I aave to agree with some of the comments on the flying in that video, it looks horribly dangerous, ill considered and frankly cowboy. I've never actually shot pig from the air but have chased Warthog many times with a view to borrowing a rifle and having a desert barbecue, as did my colleagues at the time. The technique is as described above, sit on their rear quarter and they'll just trot along offering a clear and easy shot. Get too close and they spook and double under you or swerve to the side. 40-60 feet away was probably the distance to keep them in a straight line. We found we could direct them where we wanted them to go reasonably well and it was easy enough to keep splitting a group until you'd cut out the one you wanted and got him on his own (we didn't fancy the idea of his mum and dad coming looking for him as we were roping him up).
Sadly we fell foul of silly notions that the guards might get offended that we were eating pig...we weren't planning to offer them any. Pity. I'd love to be able to tell tales of hunting Warthog with an AK from a Jetranger!