Lohollan

In Celtic Mythology, Fomors were the first inhabitants of Erinn, they were there when everyone shows up, It's my opinion that Mores believes that Fomors are not a species confined to Erinn alone, and I would guess he even brings up the other world of "Lohollan" because if his book of Revenge ever made it there, he would hope that they read it.

I can't say for sure how it all relates to the in-game mythology. but I would guess it would relate that there are likely Fomors outside of Erinn, and that the game recognizes Lochlann/Lohollan as a canon location.

If that didn't answer your question, I apologize.