Seems to me it wound be likely that the dog was probably loaded with blanks, or the equivalent. The guy might have soiled himself, but would likely survive. Somehow I doubt that military surplus would still have live ammo or lethal systems.
hopefully
The natural form of a dog is a lethal weapon. I sometimes think about this when I'm playing with my dog and my hand is in her mouth. Some part of my hind-brain should be screaming its head off at that.
A kid stuck his finger in my dog's eye the other day. She snapped at him. He didn't move his hand at all and she took the whole thing into her mouth. Thankfully the natural state of my dog is "full safeties on". She left the kid standing there with his hand soaking wet and still in the same position, but totally unmarked. His mother complimented me on my dog, and then told the kid he was lucky he still had a hand.
If I had "turned safeties off", the kid would have been a bleeding mess on the ground. My dog doesn't have any "live ammo". She doesn't need it. She's a direct descendant of one of nature's great killing machines.
If the dog in the story was an accurate replication of a dog, it's very existence is lethal.