This is nonsense. I've met Asians that sound black. They exist everywhere in the south.
Similarly, I have met black men and women (ironically also in the south) who sound indeciferably white. One had a white redneck accent while the other was raised by whites and she sounded like a valley girl (despite being from Kentucky)
While in London, I encountered pakistanis who sound exactly like black londoners .
Anybody of any ethnicity can sound like anybody else, based on whatever culture they choose to partake in. Especially if they do so early in life. Black people obviously partake in black culture and will sound black, but those black people who do not partake, will sound nothing like black people. Folks of nonblack ethnicities can sound like us too, but very few of them embed themselves in our culture , relative to how much they embed themselves into white ones.