My headcanon is that the Disco Klingons are augmented augments. They're descended from victims of the Klingon augment virus, but DNA from another species was used to overwrite the human DNA in the augment virus, perhaps an archaic Klingon species (like Earth's Neanderthals or Homo erectus), or even another living species on Qo'nos that's a close genetic match to the Klingons (like how a chimpanzee is a close match to a human). Or maybe a little bit of both.
Again, that's just my headcanon. I'm NOT trying to suggest that that's what actually happened, or was the writers' intent.
A failed attempt to correct the Augment Virus, even, that went too far in some cases. Overkill. In the attempt to regain their Klingon heritage they overshot their goals.