It's likely just a semantic choice - I mean, you still have the scene where she flickers back and forth between Eos and Selene, no?
...I've got nothin'. If they are indeed from "another world," I wouldn't even know where to start, and the game itself is still really fuzzy about how we're supposed to categorize aetherial entities (primals vs. summons vs. elementals vs. sprites) in the first place. It could just be the word choice. Though, "otherworldly" sometimes just means "seemingly not of the natural world," which is synonymous with "etherial" and in Eorzea "not of the corporeal" often means "of the aetherial."
I'm still wondering if there's a secret second class of the TRANSCENDENT regnum for non-voidsent aetherial entities that they just never told us about... too bad I never had a chance to test the early 1.0 "Eluder" abilities on elementals.
