Well, I might get some flak for this comment, but I totally understood what he was doing. When I was 12 I got my first horse and -unbeknownst to me- she was a monster when it came to having her feet touched. Her hooves were absolutely awful when we got her so one of the first things we did was have a farrier come out. She beat him up pretty good, but I learned a lot that day. Being a farrier is a dangerous job because it doesn't matter what a horse's manners are like: the hooves still have to be taken care of. Watching the video I saw a highly reactive and un-trained horse acting very similar to mine. Some of you said that the horse was reacting to someone new asking it strange things, but I don't think that's an excuse. The horse obviously had been allowed to get away with behaving in this way. While I wouldn't have gone about it the same way this farrier had, I also understand that for whatever reason these people have not put time into this horse yet, but still expected him to be shod. The farrier has to do what should have been done slowly over the course of several weeks -or months- in a single day. So, yeah, it's not pretty and gentle, but it gets the job done without hurting the horse.
In response to the OP, who was asking how what he was doing applied to shoeing: maybe I can help explain. When he was pushing against the horse he was measuring how it reacted to pressure. In order to shoe it, he would have to be in close vicinity of the animal's hooves, and he needed to know how it would respond. The bag flapping was a safe way to desensitize it to the contact and noise/movement while staying out of range of the hooves. As the person in the video said: "He will kick you." It was the same with him patting the horse all over and jumping up and down around it. The horse needed to be less reactive before he could safely even think about picking up the hooves and shoeing them. He ran the stick down the legs to get the horse used to something touching them, and so that later he could pick the leg up get the hoof without the horse freaking out. Even though I wouldn't use his methods, I can still respect them. He shoes the horse and in the end the animal walked off calmly with neither of them being hurt.
All I can add is that I really hope those people work with that horse a whole lot so that the next trip will be less eventful.