Try not to read too much into it. In this story, they are Terrans. People from Earth are Humans. As in people from Pantheria are Pantherians. And Echo (Ecko) is a Teldarian from Teldar. Acladeans from Acladia.
If you want to really get that technical about it, the Pantherians and the Acladeans are in effect a society that have joined forces to support each other. Therefore, the Acladean Rebels are still rebels since they defy their own kind as well as the Pantherians.
