If this really was the first successful contact, I don't quite understand how the language of these people is the same as/similar to other Andaman island/Indian languages. Context: "Nariyali Jaba Jaba".
Scott suggests that we might tend to think that isolated people have been there for millennia and have no idea that there are other human beings, but that very often they just wanted to be alone, or not part of a particular society. (And for those who deliberately left, they may have left behind things like governments, agriculture, and metalworking technology.)
It does seem like we have a tendency to say "ooh! unchanging primordial antiquity!" and not remember that human migration is one of the greatest constants of human history, and everyone has a story about how they got where they are.