From what I gather by reading all the various info you can find in-game, Makedonians were NOT Greeks, but a very Hellenized group of people just to the north (which is geographically correct). They also had strong ties to the Thraikian tribes and other tribes (I would presume the various Getic and Illyrian tribes are also in there to a lesser extent) and could probably best be though of as Greco-Thraikian rather than "true" Hellenes, ie pure Greeks. Thus he can technically have the trait, which just means he hates Greeks, who in their turn probably look down at these "upstart" Makedones who "stole" their ideas and such.