Are you surprised? You shouldn't be. Most of the elements of metal music have been part of Maori culture for centuries.
I probably shouldn't have been, as you're right. I just hadn't considered it before, and then they turned up in my YouTube suggestion list.....
Guess I've become easily excitable these days
Check out Tenger Cavalry. Mongolian horde metal.
Listening to them now, digging the throat singing