I think the "one-drop rule" has cast a long, long legacy on racial identification.
I'm sure it isn't "just you", but this is wrong.
Gebru was born in Ethiopia to parents from Eritrea, a West African nation whose inhabitants are often much lighter skinned than the "African" stereotype.
Wikipedia seems to confirm that: "approximately 40% of their autosomal ancestry to be derived from an ancient non-African back-migration from the near East, and about 60% to be of local native African origin "...
Not to mention there's no single black race... Africa has more genetic diversity than the rest of the world combined... Calling them all simply "black" is even worse than calling everyone else (Europeans, Native Americans, Asians, Australians, Polynesians) by a single term (brown/white/yellow people, oh man, that' terrible)... just doesn't make any sense.
Imagine a group of people who discriminate all red headed people. Makes as much sense as discriminating all people of a certain skin colour.
To answer your question: in this hypothetical world where red heads have a hard time: imagine someone being fired for fighting for the rights of redheads while actually looking blonde with a tiny amount of red in their hair colour! That's the situation we seem to be in.
Personally, I think that Gebru is absolutely correct to categorize herself as a Black Woman for purposes of fighting against the discrimination she experiences.
So apparently this woman is black in the USA: https://en.wikipedia.org/wiki/Rashida_Jones
People still use this one-drop rule, like, in the 21st century?? What the hell?!