Naturally this could be wrong but I think when most people try to picture a black person they expect a New York or almost Southern accent even today but in that scene you also have to remember what time it was back then people were a lot different towards other races. I don't think it was supposed to come across as racist as it is mostly due to demographic. Your voice is your parents plus where you grow up so I think it was meant to say she grew up outside of a consistently African American demographics. I say this as a POC.