Well the pink one could be a sub-servant of Leviathan or perhaps a pet of the Shangins (Much like the Almaja have Drakes or the Xali have Dogs) which would make sense.

Though on a note when your doing the Mini-Ifrit quest in Limsa, the GC Quest NPC does mention that Limsa had successfully defeated Leviathan on it's own making me wonder if they defeated the Pink one instead of the Primal itself.