Should I have put "white person" in quotes? Should I had phrased it like "what would commonly be called a "white person"".
I felt that would be overly pedantic of me and besides you are missing the point: "white people" do exist, it's just wrong to assign any shared attributes to them other than "looks like a white person". And by the way, I don't mean "wrong" in any kind of moral sense, I mean wrong in terms of "factually incorrect".
If he had talked about ghosts instead of "white people" would I have sounded awfully silly if I had said "ghosts don't exist. Ghosts are frequently just photography artifacts or sleep paralysis hallucinations." because I used the word "ghosts" in the next sentence?
So you think that the pre-scientific idea of categorizing people by skin colour and nose and eye features is valid and that the scientific understanding from genetics is "nonsense" that I "want to believe"?
That's both ridiculously presumptuous and ... well, stupid.
Your own mind subconsciously knows the nice ideas you want to believe are nonsense. Interestingly, that is analogous to the otherwise open-minded subjects of the study at hand who subconsciously favour their own.