He refers to the object as "it", so I don't think he will be talking about the horse. But a new question arises, "Stuck a feather in his hat and called it macaroni"! This could be taken as: A: He's calling the feather macaroni B: He's calling the hat, combined with the feather, macaroni C: He's referring to the entire action of placing his feather into his hat as "macaroni". In my opinion, I would say the hat would be considered macaroni.