Your literal place of birth is not where you are from when you're talking about race.
There are black people who have been born in America generations going back 400 years. Still African though.
Discussion
Okay and what gene tells you that you’re African? And which part of Africa? That place is huge. Which village? Which family bloodline?
Think of it like a fingerprint. There is no one gene, but by assessing a collection of them against prior examples of people who are native to a region you can trace it back.
And by collection I don't mean like 5, I mean thousands.
You could find out the family bloodline and the village if you had a reference to go against. Hence how we know who was descended from Gengas Kahn and other ancient historical people.