I don’t really see that- there’s a difference between a contiguous culture and genetics. If you’re living in western Italy, you might be descended from and still inhabiting the area of the ancient etruscans, but it doesn’t mean you have the same culture. One could make an argument that you’re from the Roman or florentine culture, but you are from a culture that’s younger than etruscan culture.

Aboriginal Australians (I’m not sure about Torres Strait Islanders, so I hope that’s the right terminology) have been practicing elements of the same culture for longer than any other civilization we know about. You raise an interesting point about them now vs them 1000 years ago, but I grew up wildly differently from how my father did, and we’re still part of the same culture. It’s sort of like the question of stepping into the same river twice- the water is different, but it’s guided by the same constraints.