He links to some census statistics from Wikipedia about the demographic makeup of London over time, and then says:

> In 2000, more than sixty percent of the city were native Brits. By 2024, that had dropped to about a third

Those figures line up with the "White British" row of the table: 59.79% in 2001, 36.8% in 2021.

So it seems pretty clear his definition of "native Brit" means "White British person".