Why did the boy return the house?

Solution
The boys, Mourad and Aram, returned the horse to the farmer Byro because their conscience was pricked by the latter's conduct. When John Byro accidentally met the boys near the Fetvejian farm, he saw his horse with them. Byro even counted the horse's teeth, however, he still refused to believe that the horse was stolen by the boys. He said that he knew about the honest reputation of the boys' family, and so, he will trust that the horse might be a twin of his lost horse. The boys' conscience was struck seeing Byro's trust and therefore, they returned the horse the next day.