Could you elaborate on what you mean exactly? It's been a very long time since I've looked at that book.
In general, I'm thinking of the technique of encounter design which is about pushing the players (via the fiction in which their PCs are embedded). It's using the story elements that are part of the game and genre as deliberate devices for creating certain responses, rather than just (in the way Mearls
did talk about) thinking of the gameworld as some organic whole. In Forge-y language, I'd say that Mearls has canvassed a gamist approach, and a simulationist approach, but not a narrativist approach, to encounter design.
In Cthulhu, this might be advice on how to use family members as cutlists' victims (and cultists).
In a superhero game, this might be advice on how to use sidekicks/signficant others (Lois Lane, Jimmy Olsen) as victims, or antagonists (if Lois is trying to learn your secret identity).
In D&D, this is about using the different magical/mythical story elements: demons, devils, undead, elementals, genies, dragons etc. What sort of theme and feel does an encounter with that sort of creature invoke? What PC story components will it pick up on (eg undead encounters for Raven Queen worhsippers, or giants vs dwarves, as easy examples)?
I hope this also makes clear - I'm not asking for anything especially sophisticated or hifalutin in my D&D. I'm not looking for anything that goes beyond standard and classic fantasy tropes and themes (loyatly vs betrayal, honour vs cowardice, law vs chaos, mortality vs immortality, etc). I'm just looking for the designers to talk about how they see the monsters, and the way they are designed as story elements (which includes the mechanical expression of their story significance - one of my favourite things about 4e monsters), instead of putting all only in ingame terms and leaving players to work out the meta stuff themselves.
A non-D&D monster book that illustrates the sort of approach I'm talking about here is the Burning Wheel Monster Burner: each monster entry has backstory/ingame explanation,
plus metagame description of the monster in story terms (how you might use it, how you can expect the PCs (and their players) to relate to it, what the likely consequences and ramifications might be, etc)
plus mechanics which often include suggested combat tactics as well as the mechanical expression of its personality (in BW this includes Beliefs, Instincts and some Traits).