You don't need to be extremely observant. Many years ago I observed a black man peeing on a tree right in front of Rotterdam Central Station in Netherlands in a broad daylight. While it doesn't necessary mean that native Dutch wouldn't have done the same thing, something tells me he was not from Dutch culture and you don't need to be an expert to guess. Was it about skin color or his behavior?
Time of year, at a guess.
Zwarte Piet pissing on a tree is more of a Dutch Christmas tradition.
Then he goes on to point out more than sixty percent of the city were "native Brits" in 2000, but that number corresponds to the White British categorization.
Ergo he's conflating White British with native British.
He also said "A statistic as evident as day when you walk the streets of London now." Maybe he is extremely observant, but I don't think that follows unless he is talking about skin color.