The question just forces the person being asked to think, "Would I mind if this researcher saw me as someone who would mind if a foreigner lived next door to me?" And the degree to which this second-order question matters depends heavily on social mores.
Japan is a country where people are expected from a young age to compartmentalize their tatemae (external appearance) from honne (true thoughts), and consider it perfectly normal to do so. So I wouldn't be surprised if they were simply better at hiding perceived-as-negative sentiments from naive researchers.
Koreans, on the other hand, admire Americans and Western Europeans but look down upon Africans and South/Southeast Asians, and often express outright contempt for the Japanese and Chinese. Depending on their political views, they may even feel socially compelled to express a hatred of one or another nationality. Meanwhile, Korean culture doesn't acknowledge the tatemae/honne distinction, which makes it a lot more difficult for people to compartmentalize.
tl;dr: We're all racists, but some forms of racism are easier to measure.
The question just forces the person being asked to think, "Would I mind if this researcher saw me as someone who would mind if a foreigner lived next door to me?" And the degree to which this second-order question matters depends heavily on social mores.
Japan is a country where people are expected from a young age to compartmentalize their tatemae (external appearance) from honne (true thoughts), and consider it perfectly normal to do so. So I wouldn't be surprised if they were simply better at hiding perceived-as-negative sentiments from naive researchers.
Koreans, on the other hand, admire Americans and Western Europeans but look down upon Africans and South/Southeast Asians, and often express outright contempt for the Japanese and Chinese. Depending on their political views, they may even feel socially compelled to express a hatred of one or another nationality. Meanwhile, Korean culture doesn't acknowledge the tatemae/honne distinction, which makes it a lot more difficult for people to compartmentalize.
tl;dr: We're all racists, but some forms of racism are easier to measure.