With ALL due respect (seriously), this is just a misconception of yours.

When you write software to solve a problem you start with as little as possible details such that when you read it, it would only talk about the business logic. What I mean by that? That you abstract away any other stuff that does not concern the domain you are in, for example your first piece of code should never mention any kind of database technology, it should not contain any reference to a specific communication layer (HTTP for example), and so on.

When you get to this, you have summarized the "spec", and usually it can be read very easily by a non-techincal person (but obviously is a "domain expert") and can also be very testable.

I hope this helps on why the author is right 100%