Dusty has never owned a horse before. He once had a dog, but a horse is different. This horse is even different to other horses.
Freckles is the smartest horse Dusty has ever known. Even at first, while still wild, Freckles knew exactly what he was doing. He tied Dusty to a tree until Mr. Callahan came running, and from that day on Mr. Callahan became convinced that Freckles was better at keeping Dusty out of trouble than anyone else.
Freckles looks out for Dusty and asks nothing in return except food and water. For that, Dusty owes him everything.