I usually classed many people as foreigners and immigrants back in London >_>

And the us versus them mentality is with every culture. I don't know why people single out Japan or Koreans for this. Go to a majority of any country and their families will see the foreigner as an outsider, no matter what you do. It happens in other Asian countries like Pakistan, India, Bangladesh, even African families do the same for white people.

Yeah you may see the occasional "White foreigner in country" video where they bend over backwards for them, but thats to keep to their values of treating guests like King. Get deeper into the levels of family and community, and they will definitely be treated differently. Trust me, I'm Asian and I know this on a fundamental level.

Its not just a Japanese or Korean thing and its kinda annoying people just keep pointing those two cultures out as if they're the only ones that do it. Hell, the only reason why its not seen more in the publics eyes in places like America or Britain is because those countries are more multicultural now due to their more relaxed borders and people's desire to live in a first world western country. But I guarantee you, put a black family into a gentrified neighbourhood or vice versa in the west, and see how they're looked at differently.