The childhood of Alexander the Great

This tapestry, just under forty square meters large, describes some scenes from Alexander the Great's youth, starting with the arrival of the cruel horse Bucephalus - who, before being tamed by Alexander, ate human flesh - the clash with the enemy Pausanias, the death of Philip of Macedon and the passing of the crown to his young son Alexander.
Looks like "the cruel horse Bucephalus" had pointy teeth and weird horns on its head, as well as eyes that were too far forward for a horse. In fact, of the five horses I can make out, only one does not have twisty horns on its head. I assume that's Alexander on the "horse" that's breaking its chains. It makes me wonder, when the artist does such a good job portraying the people, how he could get the horses so wrong? Had he never seen a horse? Were horses different back then?