They were Maenads, but not sent by the leadership of Pangaea. We are half a world away from Caelum, and have no way of sending such a force there.
We assumed it was a random event, much like the occasional attack by Ermorian cultists, though we are sure most would find Maenads more pleasant to look at, at least, before they are torn to shreds by them.
I'll have to make a mental note on the effectiveness of Tangle Vines against high defense creatures though.