You're ignoring GPs first sentence: "It's been my experience that you can't tell who's smarter than who by what they do for a living." This first sentence indi

You're ignoring GPs first sentence: "It's been my experience that you can't tell who's smarter than who by what they do for a living." This first sentence indicates that they are writing about individuals with a vocation, not a group average. Statistically, in developed countries, any given manual laborer is likely to be less smart than any given venture capitalist, but Elon Musk, for instance, has been both. If you'd randomly picked him, in December of 1989, from the pool of manual laborers, you would have been wrong.