Think of other white guys with black backs like Dorian Yates and Jay Cutler.
In fact, Yates may have the best back development of any Mr Olympia...period.
Of course, Haney and big Ronnie may have something to say about this

I don't think it's "racist" to speculate if some ethnic group has a body part advantage.
For example, white and Asian men MAY have better calf development then blacks?
BUT, when you get the best, individual pro physiques, no one nationality has a clear advantage.