I had the same question (the article isn't that great, it comes from a "bathroom reader"). From previous reading about this fascinating topic, I think they must've established the dates for the other tribes and other islands of the Andaman chain, and then just assummed North Sentinel was similar. I think that's a fair assessment because its size and location is not atypical, so there's no (apparent) reason to assume it was settled earlier or later than the other islands.
This of course begs the question of how they got to the island. In the past, when sea levels were lower, there may have been land bridges between islands and the mainland (not sure 'cause I haven't studied the bathymetry). Another explanation for how they got there is that they did have sails or oars in the past, but they were forgotten over time.
This of course begs the question of how they got to the island. In the past, when sea levels were lower, there may have been land bridges between islands and the mainland (not sure 'cause I haven't studied the bathymetry). Another explanation for how they got there is that they did have sails or oars in the past, but they were forgotten over time.