The commentary links increasing qualification with greater particularity, less expectedness and potential information value. A generic event may fit many circumstances; suitably chosen qualifiers identify a more specific occurrence.
Stage 1: Someone read a book.
Stage 2: Zayd read a particular book.
Stage 3: Zayd read that book at a stated place and time.
The idea of unusualness does not mean that a report is irrational. It means that fewer events satisfy its precise specification. Truth and relevance are still essential to its rhetorical utility.