No, this isn't a bash on our boarding facility.
Yes, we are positive the horse was injured from the feeder - his blood from the gash was on the feeder.
The horse out of alignment cannot bend his neck to the right or left and cannot be ridden from his sore back at this time. Yes, the vet is convinced the issues are from twisting and stretching to get hay from the feeder.
Sorry - I have been in the business long enough to see horses do some pretty stupid things. Horses can have a yeehaw momement fall and do the same thing you describe above. We had a horse unable to lift it's head for two days. Vet was out and said he probably fell and pinched a nerve. Unless it was witnessed - nothing else to prove.
My own horse was kicked in the chest and had a gash that required sutures. We saw the kick - or it would of looked like an injury from the fence or round bale feeder. After the kick, he went to eat. Blood on the feeder . . .
Again - are you are absolutely positive these issues are a result of the feeder? FWIW - we have cattle panel feeders for our beef herd. They are pretty darn tough. They have to be to stand up to the pressure.