The reason it's called "Gifted" is because you get born with it, just like your skin color. I didn't choose to have a high IQ. Frankly, with the way people have treated me in life and all the pain I've gone through due to it, I'm not so sure I'd want to be this way. I'm sure you know that feeling.
You want to explain performance differences in racial groups, look at complex trauma and cultural phenomina. Conduct an similar ACE study in the south-side and see what you get.
I think what you're going to find is 50% of the population has generational complex trauma they are trying to escape, and their outcomes would be improved draumatically by specialist intervention and I think one that is done, you are going to find out IQ isn't altogether different between racial groups in a country like the US.