Some say that the Swedes had a whole lot of dry fish when the Vikings attacked and rather than give the Vikings their fish, they tossed it all in a barrel of lye, but that didn't stop the Vikings. Another story is that the Swedes had a whole lot of dry fish when the Vikings attacked and tried to poison the horde by soaking it in lye and then serving it to them for dinner. I would guess it was for treating hides and that the first lutefisk maker saw what the lye did for the dried hides and knew that the hides, with the lye washed out, could be chewed without killing you. She took a long look at the hardly-digestible dried fish she had been subsisting on. This is completely a Saint Report speculation but it sounds at least as reasonable as the other theories.
Human beings are amazing creatures.
No other species could make enough weapons to blow up the world and also invent lutefisk and sour herring. If we ever find ET, he sure will be impressed.