Unexpected indeed, but the fact that she actually exists in the game and therefore is canon, surprises me more. They really put effort in choosing and designing creatures/things to be anthropomorphized.
IIRC, that's because Mine was somewhat uncomfortable with the whole gacha rarity thing for extant animals for some reason, and so created the cryptid, mythic and extinct Friends to fill the tiers. Take that with a grain of salt, though, as I cannot remember where I originally heard that.