Since Europeans were first to discover and settle on the islands, wouldn't they have a greater claim to "indigenous" status than later ethnic groups? I genuinely don't understand, having had a quick read of the history, how your narrative of "colonialism" (in the pejorative) fits the actual timeline.
https://en.wikipedia.org/wiki/Chagossians
> The Chagossians are a mix of African, South Asian, and Malay descent. The French brought some to the Chagos Islands as slaves from Mauritius in 1776. Others arrived as fishermen, farmers, and coconut plantation workers during the 19th century. Under international law, they are the indigenous peoples of the Chagos archipelago, as they are descended from the earliest human settlers of the islands.