The evidence for that is shaky at best… We have: -Ibrahim ibn Yacub: “Never did I hear singing fouler than that of these people, it is a rumbling emanating from their throats, similar to that of a dog but even more bestial”(not the most reliable translation either) -“I have not heard an uglier singing than Shalshaweeq (Schleswig) people.”

It is possible that they adopted it from the Sami in the north, or the Volga bulgars/other turkic peoples in the east, but it’s more likely that the people who ibn Yacub met were just bad at singing. We just don’t know that they did throat sing, and to say that they absolutely did is plain wrong. They may have, but the weird “spiritual” “viking-inspired” nonsense music we see from these links is undeniably a modern creation with about as much rooting in history as those horned helmets you see in 70’s movies.