A human-length neck massage is not adequate for a horse-sized neck.
You know how they always say your pets are only nice to you for food? That's absolutely not true. They are nice to you because they know you can get all those hard to reach spots and scratch the hell out them with your dexterous people fingers. This horse is not letting his rub machine get away if he can help it. If that man dropped over dead right now, the horse wouldn't eat his face. He'd roll on the guy's hands until he ground them into the stable floor.
Side note: that horse has such a long neck! It's almost as long as a giraffe's (this is not in any way accurate, but it feels true when you watch the video).