The horse has had a Vet visit, at least once. So its not like he was hurt then tied and left alone.
I have read and re-read the article, and the attached statements from the owner and the attending vets, and this isn't the impression that I have gotten. As near as I can tell, events transpired in this order: one of the horse's owners dropped in on the trainer's place, unannounced. He was appalled at the condition of his horse, but, not having a trailer with him, couldn't remove it at that time. He returned the next day, with another owner and a friend. They removed the horse, and took it to a vet in the area. That vet treated the wounds on the horse, removed bone fragments more than 2" long from the horse's jaws, gave the horse a body score of 3, and sent the horse home. A second vet saw the horse after it had been home for a while. He assessed it as having gained some weight (body score of 4,) and noted the healing of the reported injuries.
I agree, we don't know how long the horse had been tied, but one of the owners says they gave the horse some water just before they loaded him, and he drank it, so he was evidently thirsty (not that that means anything, one way or the other.) No, we don't know who inflicted those injuries on the horse, although the one vet seems to feel that the responsible party is very long-legged (is this big-name trainer a tall man?) Nothing I read indicated that the trainer or his employees had treated, or sought treatment for the horse's injuries, the only vet care I read anything about was done while the horse was in the owners' hands.
I also agree, the OP jumped to a conclusion when they read the article, that the trainer is the one who did this to this horse. I noticed that the author of the article was careful not to do the same thing. Without more evidence, we can't be sure exactly whom the shoe fits, but with two horses in the barn in very similar condition, I wouldn't send any animal of mine there!