I disagree since the book is using a functional programming language to advance the idea that CS is about procedural epistemology as opposed to the declarative stance of maths.

The idea that a 'procedural programming paradigm' exists in contrast with a 'functional programming paradigm' is blogspeak imho.

My understanding agrees with namaria's. I'm inclined to think that, in the passage you provide, `imperative' means `pertaining to processes' (where processes are those things described by procedures; or, perhaps better put, the meanings of procedures).