You could argue that the author is a knowledge worker as well. He talks about how his job requires him to know and learn about a huge number of things, then he applies that knowledge to solve a problem. Yes, his job is miles away from writing position papers for a think tank or falsely summarizing complicated research in a company, but it is pretty far away from laying brick or hauling gravel as well.

In the end, I think we agree. Shitty jobs where you are not accomplishing Good Things suck and should be avoided. You can find rewarding jobs in lots of places, not just the ones our culture usually promotes. People should consider some kind of trade more seriously. I don't think he is trying to claim that manual labor is sweepingly special and more rewarding than other professions, and I think he is right not to do so. Writing code is undeniably knowledge work and I know that I derive great satisfaction from being able to hit the right combination of keys to make what I imagine appear on the screen. Many people I know are knowledge workers in some way and they have found real fulfillment in those professions. Research, Psychiatry, Writing, etc.

It is very fulfilling to make things with your hands because the results of your effort are so recognizable and tangible, but I think that many have found equal satisfaction in other fields.

To each his own.