Why couldn't Mourad buy a horse in "The Summer of the Beautiful White Horse"?

At the beginning of the story, Mourad, the narrator's cousin, appears at the narrator's window in the early hours of the morning astride a beautiful white horse. The narrator, Aram, is amazed to see the horse for two reasons. Firstly, he is amazed because he has always had a longing to ride a horse. Secondly, he is amazed because he knows that Mourad could not possibly have bought this horse, and thus must have stolen it.
Aram explains why Mourad could not have bought the horse when he says, referring to the tribe to which both he and Mourad belong, "We were poor." He then goes on to emphasize the point when he says, "We had no money. Our whole tribe was poverty-stricken."
Despite the fact that he can not afford to buy a horse, Mourad proves to be a rather accomplished rider. He later tells Aram that he has "a way with a horse. I can get it to want to do anything I want it to do."