Yes, I have actually read about all that. Indians settlers have now settled on the Andaman and Nicobar Islands and most of the locals have now come into contact with modern civilization. The only exception, as you say, is the small North Sentinel Island.
I have no doubt that those people are descendants of one of the earliest human migrations from Africa into that part of the world. The question is though if they ever traveled through the Arabian Peninsula like almost all other humans before they migrated to the remaining world or whether they just took right off from Africa by sea all the way to the Andaman Sea.
Have any of you Indians visited the Andaman and Nicobar Islands? How those their indigenous cuisine differ from the Indian one - in this case South Indian? Is/was it not quite primitive?