Biology: I’m not saying those are the numbers (that WOULD be ridiculous), but the concept that maybe the number of people auditioning is disproportionate is not far-fetched at all.
The type of person who would try out for Jeopardy in the first place probably has at least a relatively decent ability in the first place- remember, there are so many factors that go into selection, whether logistics (can you take off from work long enough to try out/film, are you within a reasonable distance of the place where they shoot), personality and photogenicity (yes, that’s a word, I googled it just to make sure), etc. Intelligence and knowledge are part of it but not the entire thing.
I’d be careful basing this off that book, though. The APA did an investigation of it afterward, and while most of the ideas were found to be true, many of the ideas concerning race and genetic intelligence were discredited. Even so there are plenty of books debating the concepts behind the bell curve when it comes to intelligence.
While that is always the case in science, don’t rely on it like the law.