It's the problem of descriptors. We use human race to distinguish ourselves, but it's, as Melina talks about above, a species issue. So, in SF, you have species with planetary names (Vulcan, etc.), but here, we have only the silly Earthlings. We don't generally go for Earthers. The tag that we provide, then, for our planetary species identification is human (race). Which doesn't equate to cylon as a species/race, either. They could be Caprican cylons, or maybe Kobolian (Kobolite?) cylons... or something else, but they would still be semantically equivalent to human if you were saying the same thing about humans.