That an interesting “unwritten law” drawing first blood is rightful ownership, not sure that’s universally agreed upon everywhere. Sure, if it was me that put down your gut shot buck, I’d give it to you, but that’s more of a kind thing to do for a kid. Someone mentioned a gut shot buck is a dead buck, sure but it can live up to 12 hours in agony before it dies, if it’s recovered before meat is spoiled or eaten by predators.
To keep this as an apples to apples comparison, if I’m anywhere in North America and make a bad shot, gut shooting a deer and it runs off half a mile and another hunter kills and claims it, I wouldn’t feel that deer is mine, just my opinion. I’m sorry that traumatized you as a youngster, I’m sure it would’ve been the nice thing to do for him to give you that buck.