Did the boys return the horse …

The story gives no indication that the boys were afraid of anyone or anything. Hence the return of the horse was not directed by fear. Secondly, they were not at all consciencestricken. They did not feel any pangs of repentance or remorse at their action of stealing a horse solely for the purpose of riding it. The narrator makes it amply clear when he asserts that stealing a horse for a ride was not the same thing as stealing something else, such as money. For him, it wasn't stealing at all as he and Mourad were so crazy about horses. In his opinion it would become stealing only when they offered to sell the horse, which he knew they would never do.
The last phrase gives a clue to their mental make up. Mourad had the horse for over a month when farmer John Byro visited the narrator’s house. They retained it for two weeks more. Mourad outrightly rejected the narrator’s suggestion of keeping the horse any longer. It was his family pride that would not let him steal. He decided that the horse must go back to its true owner.
The meeting with John Byro proved conclusive. He praised their family for its honesty. He trusted the boys as he knew their parents. Hence in order to uphold the family tradition and reputation, the boys returned the horse to its rightful owner.