Blackanese...really, why are people always so quick to make assumptions about race?

so i was getting my make up done and the lady says "you have the prettiest slanted eyes...are you blackanese?" and she was beng totally serious. Its not the first time I have been asked this question. People always assume because I have "slanted" eyes and curly hair that Im mixed with chinese (blackanese) but both of my parents are black. Can someone help me understand? I mean why do people assume they can tell someones racejust by looking at them?