Renaming Bats
Language evolves over time.
The original world for “bat” probably meant “flapper”.
So they are called ‘bats’ because hey ‘bat’ their wings, like bats are called ‘bat’ because they flapped their wings.
They could call them something else, like ‘flapper’ or ‘flutterers’ or ‘drakebats’, but I don’t see any reason strong for it, unless there’s also actual ambiental bats that look like Earth’s bats like GW1 had.
I haven’t seen any in GW2, though.