I agree with Horsesdontlie, franknbeans, and cherie. There is nothing wrong with the method of the rope around the flank (or even around the butt and under the tail), you just have to know how to properly use it for it to be effective. That is not something I would do on a typical young horse because I don't want them to buck even once if I can avoid it. However, on those that are very willing to buck, it works.
In that video, it is really hard to see enough to make a final judgement one way or the other. I've dealt with some horses that had been spoiled and they would react to a regular saddling much like this horse did to the flank rope; they would start bucking and come right toward you because that is what they'd been taught. If you didn't either get yourself out of the way fast enough or get them away from you, they were perfectly content to just buck right over the top of you. That may be the type of horse he's dealing with, we don't know.
yellow editing done by someone just looking for a "
OMG" reaction from people who don't know better. The fact is, anyone with a lick of sense knows that you can't tell anything about someone's training from a video of 1-5 second clips strung together. Sometimes it gets dramatic and everything doesn't always look all smooth and perfect.