This guy doesn't know how to measure programming ability, but somehow manages to spend 3000 words writing about it.
To be fair, you can spend a great deal of time talking about something and make progress on the issue without solving it.
Another reason to waste a lot of time talking about a problem without reaching an answer is to elaborate on what the known unknowns are and speculate about the unknown unknowns. Indeed, the point of this article seemed to be to advertise the existence of unknown unknowns to "recruiters, venture capitalists, and others who are actually determining who gets brought into the community."
So he doesn't know......programmer ability might actually be a bi-modal distribution.
Perhaps ... but that would imply that one does not transition over time from one hump to the next or if they do, it's like flipping a light switch. When I read this I assumed that he was talking only about people who know how to program and not "the average person mixed in with programmers."
If he had collected data to support his hypothesis, then that would have been an interesting article.
But you just said there's no way to measure this ... how could he have collected data? What data set could have satiated us? The answer is quite obvious and such collection would have been a larger fool's errand than the original article's content.