I have no clue what those techniques were supposed to train the horse to do??????
If they are done properly, then they desensitize a horse to pressure all over their body and teach them that they aren't going to get hurt so there is no reason for them to buck. I've seen lots of people get bucked off (and some of them hurt bad) because their cinch hobble broke on their saddle and their back cinch slid back into the horse's flank, or like Ledge said, a horse gets a rope under their tail during ranch work or roping. If a horse has never had pressure there before and learned that, while it may be uncomfortable, bucking/kicking is not an appropriate response, then people can get seriously hurt.
It's not something that you do instantly on the very first time you handle them, they are prepared for it first. I usually use my hands at first and, after they are used to being touched everywhere, I will apply pressure to one side of a horse's flank. Most of them just look at you like "What are you doing, you nut" or, at worst, pin their ears and pick up a hind leg in a half-assed threat of kicking. But, if you take a bit of time and work with them, then when you do use the flank rope, they may bring their head up and tilt their ears, but most of them don't kick or buck. Same thing with the tail rope. They are comfortable with me touching all around/under their tail before I ever bring the rope into it.
Just like this filly. She reacted better than some but it was a pretty typical reaction that I get. She kinda clamped her butt for a minute and ran a little faster until she figured out that it didn't really hurt, then she just trotted out like nothing was there. Because I did that, the chance of her bucking off her owner in the event that something gets stuck under her tail is much less than it would have been.