The author uses the term “coupling” to describe a simple program from the code’s perspective - “you need to have a good mental model of your program”. I agree, but I’d argue that more importantly you need to have a good domain model. Good design communicates accurately and a high Gulf of Evaluation/Execution are actually what makes programs feel “complex” to a user.

These concepts simplify for the user these questions: “I know what I want - how do I make the program do it?” (Execution) and “The program did something — what state is it actually in?” (Evaluation)

I believe the author was getting at these concepts, especially in their Google Drive example - how the large program has a “small” UX. Understanding the domain model provides a much stronger basis for designing user interfaces, and understanding the Gulf of Evaluation/Execution allows you to build incredibly complex-looking, large UX’s without confusing or overwhelming the user.