Right but the important part is the notes, not the notebook. It could be notecards, google drive, text files in git, sqlite, whatever. The fact that you take the notes and can find them later when you need them are literally the only two important factors here.

The "fooling themselves" element is in thinking adding sophistication beyond two those things improves the usefulness of the notes themselves. And there's some personal flexibility here too sure; if you truly can't ever find a note when you need it and adding a tagging system gets you there then that's useful additional sophistication.

I think the point they were trying to make, definitely the one I'm making, is that the line between useful system and hobbyist tinkering is a lot lower than people want to think, because they want to ascribe purpose or benefits to their tinkering. Which is where the productivity porn comes in, a framework that only values things if they are or contribute to "productivity" demands everything be productive, demands that you justify it.

But truly and honestly if you have a flat folder of text files and grep you have what you need and beyond that is tinkering. That's what people are fooling themselves about.