Why did the narrator let the dog loose?

Billy knows the hound will not give up until it finds its way home. Billy scares off the other dogs and calms down the dog. It is starving, has apparently traveled a great distance, and wears a leather collar with the name "Buddie" childishly scratched in it. Billy takes him home, feeds him and bathes him. The next night, Billy tearfully lets him go on his way. Billy wonders what displaced the hound from the country, but knows the hound will not give up on its way to its destination.