"Overtone" singing! It's just . . . . it's just
Jinksy has met this artist, Christian Bollmann, and heard his astonishing talent. The "high notes" are produced by resonances in the mouth cavity. Only the continuous bass note is "sung", in the conventinal sense, in the voice box. Jinks is hiding a lotta lights under her bushel, so she is!
Many other examples on YouTube, along with Mongolian throat singing. You'll need Jinksy to explain the differences. Christian Bollmann struck me as far and away the best of the YouTube selection of "overtone" singers.