Why do orientals get mad when you mistake them for another nationality?

Japanese get mad when I mistake them for Chinese. They act like you are supposed to know what kind of oriental they are, but I don't see white, black or hispanics like that. In Canada most of the immigrants are asian, but in the census for race population instead of grouping them as asian, they are grouped based on their nationalities. They all look alike, speak languages that sound alike, and are pretty much the same. I feel offended, because they get the special treatment. I'm Somalian but people think I'm the same as a South African who speaks clicking language. We also have different history we weren't oppressed like the other Africans or treated like inferior. But whenever I get mistaked as another black I don't get mad. In Canada, all the whites and asians are given special treatment. Personally, I don't want to be identified with other africans, because we don't have the same history. My parents tell me that Italian colonizers used to fear us, and the british colonizers didn't cross the line with us like they did with other africans, so in a way being identified with other africans gets in the way with my somalian pride. I think white people have this attitude of " they're n*ggers they aint got no difference". I'm not the arrogant type I'm just saying. If one group of people is being generalized then why wont asians get the same treatment?