I think the solid mountain was in one dimension and the colony was in another. They’d ‘tucked’ their colony inside the mountain in that other world to hide it, but the other dimension has rejected the colony and shoved it out. Colony is, hopefully, back in its home dimension and the mountain it was in is just a mountain. Our heroes seem to be in a cave in the mountain in its dimension. Wherever that is. Goodness knows what they’ll find there. A world where their kind never developed, or another species developed with a history of their own; the possibilities in the Multiverse are endless. Now, we just have to wait and see.
It’s a chipmunk so it’s neither poisonous nor venomous.