I think - cant be bothered to start a new game to check - that the attacks are attributed to Tieflings a few times in different conversations.

Kahga also says she wants to protect the Grove - and thats apparently achievable by removing the refugees... how or why is irrelevant. It just is, mkay?
Only then the ritual can be done and seal the Grove... for how long? Dont ask. Grove sealed - we safe - refugees bad.

There is also a river right there, just sayin... and one Druid bear lazily slapping fish out of it. All day.

Btw, the bears look awful. Like someone wanted to create cuddly funny looking bears but also make them angry at the same time. They looked like stuffed angry fat toys.