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".
They obviously didn't evolve there independently from other humans. They and the other tribes have common ancestry, and a common root language. I doubt anyone knows about inter-tribal contact through those 60,000 years that could have kept the languages from diverging too much.
According to the current Wikipedia article on the Sentinelese language [1], it is not mutually intelligible with Onge. This is more like what I would have expected from a strictly xenophobic and (presumably non-literate) tribe, but it doesn't square with the account in the article...
The Sentinelese and the people on Andaman Island must have been once been a single group living in the same place within the last few hundred years. The language would change somewhat after they split up, but it is still mutually intelligible apparently.
It was really interesting to read in James C. Scott's work that many uncontacted tribes are not only not primordially isolated from other human beings, but may be descended from people who deliberately separated from other civilizations because they didn't like them. (Edit: for example, they might have been slaves or conscript soldiers, or people who were defeated in a war.) Some of these people may then have significant, but maybe increasingly vague, awareness of outsiders, and a dislike of them.
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.