These tribes aren't isolated in true. Over 1000s of years, they have interacted with world outside and formed a generational wisdom and values. If 100 years back British/French came and enslaved some members, the behavior is expected.
No true Scotsman, eh? There's no reason to think these groups have had any contact with the outside world, beyond the fact that at some point they obviously diverged from whatever common ancestor we all share. Both are extremely small groups living in similarly extremely isolated locations - Sentinelese in an isolated island, Nukak deep in the Amazonian interior, far from rivers. And the Nukak's population has been decimated by common disease since they made contact, further suggesting 0 exposure to even other local peoples.
I am not a historian. Andaman and Nicobar (neighbor of Sentinelese) is occupied / use as naval base by outsiders for >1000 years. None of the Cholas, Europeans, Japan ever contacted/impacted them seems highly unlikely.
Contacts tended to be recorded. You can read ships logs now going back hundreds of years, often with illustrations. There's not a whole lot that happens in most ship voyages, so things like running into a weird group on an isolated island would absolutely have been recorded in immense detail. Of course I can't prove, beyond any question, that they weren't contacted, but there's 0 evidence to suggest they were, and immense evidence to suggest they were not. For the Nukak this is at least as true as well.
