This guy was really lucky. I have seen this dozens of times online. People at ranges or shooting matches clean their barrel between strings and end up forgetting and leaving a cleaning rod in the barrel then fire off a round. usually it results in a Kaboom. In this case it looks like the road was welded into the bore.
It’s easy to get distracted. People come up to you wanting to talk or something distracts you but you have to constantly be paying attention to everything you do while shooting.