He actually gave a very simple test that covers 99.99% of cases. If someone has pink nipples they're white. Just because it sounds funny and absurd, doesn't mean it doesn't work. It is a kind of engineer's answer that some people find hard to parse.
As for his position, I don't exactly know it and won't speak for him. I think one of the things that helped america do better than european countries was having huge resource deposits.
And what made it do better than say brazil, who also have huge resource deposits, was the stock of its people.
But how does trying to understand who is white, a grade school level question, help challenge your beliefs? Why do you have the belief that non homogenous societies will do well, when studies show that even non homogenous neighborhoods don't manage to do well (putnam and others)? Why do you believe race is only skin deep? Why do you not know about the differences in big 5 averages for different genetic groups?
How does knowing the exact cutoff challenge your beliefs at all? I don't think you are really yet trying to see things from another perspective, but I'll help you if you want to understand.