It doesn't sound to me like he would be using his own horse, so no telling how smart the horse is and he never commented on his experience with horses, so no telling how horse smart he is either.
I have however seen several broken stocks from horseback hunts, more than by any other means of hunting, so I still think it is better to be prepared. I too have ridden hundreds and hundreds of miles with a rifle on a horse and have never broken a scope or stock, but it was always MY horse, with whom I had a great understanding. There is no telling what other horses can and will do, and I have seen it..........talk to a few outfitters who use horses for a living with rifles on them........broken rifles every year, sometimes the horses fault, sometimes the hunters, regardless still broken.........