Why do people try to tell you your ethnicity?

La

So one of my coworkers mistook me for Nigerian. I kindly corrected her and told her I was American (black American) with a smile. She then goes on to ask "well maybe you're Haitian or from the Caribbean?

It annoyed me that she continued to tell me my ethnicity....as if I had no clue who I was. Why do people try to tell you your ethnicity as if you don't know who your parents and family are?

I swear I am going to start saying I am from Wakanda because these people won't accept the truth.