I think what the author is really talking about is the "build the simplest thing that could possibly work" approach, which is strongly related to TDD, but can be done without TDD as well.

It makes for a great motto, but in practice, developers often disagree about what the "simplest thing" actually is. Mostly, I think this is a function of experience. When you have more experience with a type of development, it's much easier to see the "obvious" future needs.

So in the case of a text editor, it's obvious (to me) that a giant string just won't work. That may not be as obvious to someone with less experience.

Determining what the simplest thing that could possibly work is turns out to be anything but simple!