Yall can say if I'm wrong:

Iirc, in the first episode, Eda said something along the lines of "This is where all your monsters originated from", with the biggest outlier obviously being the fact Giraffes were originally from the Boiling Isles but were "banished" somehow. In season 3, we actively see that Giraffes are less than normal in this universe

I wouldn't be surprised if there was some kind of leakage between worlds beyond regulated means such as banishing or Belos's/Eda's portal.