His dad should have held him back from shooting that shot for sure, but he may well have not known any better either. Just because we dance around on forums talking ethics all the time, and legit capabilities of weapons and interact with possibly more realistic hunters more often, doesn't mean everybody else does. Kids dad may have never watched a long range youtube video in his life. That could have been his normal practices since his dad taught him.
My dad shot a duplex reticle with a 300 win mag his whole life. Killed some animals at long range, 500ish yards supposedly, before rangefinders even came out. The whole "hold 54" over its back because thats what the box says" type of stuff. That was WAY BEFORE youtube had any influence on him, and most people back then. I bet if you ask 100 old time killers if they ever held 3' over an animal's back and took a shot, 99 of them did.
It's literally been happening since weapons were invented. Hold high and shoot. Some people have never grown from that. Despite everyone's personal ethical beliefs. Heard stories of legit archers from the past sending several arrows at 100+ yards, hoping for a hit. And same for rifleman at 500-1000 yards.
A 100 yard free hand rifle shot is less ethical that a 500 yards prone shot if you actually know how to shoot. Anyone taken a 100 yard freehand rifle shot, and kill something? I know I have, and I guarantee I have a higher probability of wounding something than 500 yards prone.
I don't think you should ever shoot beyond any yardages that you've practiced at. And you should practice a lot further than you intend to shoot. But the ethics has much more to do with shooting beyond your ability and practice, than it does the actual yardage you shot at. 30 yards with a bow is unethical if you only ever shot 10 yards. And 300 yards with a rifle is unethical if you only shot 100 yards.