She didn't redefine them. As someone[0] linked upthread (which you should have seen if you're down here) racism has a sociological definition as well as a colloquial definition. A dictionary does not define words; it records their common usage. It is, by its very nature, out of date.

Regarding your example of white people in areas with a higher black population, it doesn't quite work out. Almost any other environment, you have the advantage being white. A black person doesn't have the same luxury. They can't scoot away and suddenly go back to being privileged.

[0]: https://news.ycombinator.com/item?id=5420178