This is cute, her knowing and fondly remembering Megan and her sibs, but you also gotta think of it: there were humans, past tense, and she was there to see whatever happened. Does “I’ll never forget them” refer to Megan, Danny, and Molly… or humans as well as every other race that’s in G1 but not FIM, whose total annihilation a pre-ascension Tia could not prevent?
You know, Tia does like the occasional prank… It really could be her! (I’ve also read one fanfic where G1 was long ago and Celestia was Sundance before she ascended.)
Yeah, that’s an animation error. The princesses are the first alicorns in all the generations of FiM. Before the show started, they caused quite a stir with the old school collectors, who were all ‘wut, pegacorn finally?’