I just gotta tell you, in a friendly way, ...this makes absolutely no sense with my experience whatsoever.

I don't find
anything about the way 3e
or 4e work mechanically that I would describe as "narrative". I just don't find narrative mechanics to be a big feature of D&D in any edition.
All I can really do is refer you back to my discussion upthread of the Chained Cambion. (EDIT: It's on the other thread,
the Rule-of-3 one.)
I'll elaborate on that example in one way, though. What makes it support narrativist play (in the Forge sense, of thematically engaging and expressive play) and not just a type of simulationism (like your PC going bonkers in Call of Cthulhu) is because the players have a high degree of agency in choosing how to respond to the situation of resentment at being chained that the GM has thrown them into.
Now the thing is, the backgrounds and themes idea really intrigues me
Themes don't do a lot for me - at this stage I'm not seeing how they difffer meaningfully from feat trees - but backgrounds look interesting. (There are what seem to be some typos on the character sheets, where 3rd level features are described as coming from a background that I think in fact are theme-generated feats.)
But until we see a richer non-combat resolution system than what's been presented so far, I don't quite see how the backgrounds are going to be put to work.
One of my complaints about 4e relates to this. Paragon paths, in many cases, do a great job of anchoring the PC in the fiction (with my own group, I have a Divine Philosopher of Erathis, Ioun, the Raven Queen and Vecna, a Warpriest of Moradin, a Demonskin Adept with runes of chaos inscribed on his demonskins and on his eyelids, and a Questing Knight). But there is nothing in the skill challenge mechanics to give advice on how this sort of anchoring in the fiction is meant to play out in action resolutio. I just make it up as I go along - for example, I frequently give that Warpriest a +2 on Diplomacy checks when he's dealing with dwarven artisans and warriors who would naturally look up to him - but there is a lot of scope here for greater mechanical richness. (I'm thinking here of, say, Burning Wheel, where reputations give mechanical advantages on Circles checks, or to HeroWars/Quests, where relationships can be used as augments on other checks.)
Background features like Trade, Knight's Station, Temple Services etc seem like they should be feeding into the resolution of social challenges in some sort of way. And features like Endurance and Researcher seem a bit weak at present, without more guidance on things like how long a normal person can hold their breath (ie what benefit does Endurance really give me?), or how hard it is to find and then gain access to a sage or library (ie how useful is Researcher really?).
Also, the skills seem a little too derivative, at present, of 3E and 4e norms. "Survival" skill doesn't really tell me what it covers unless I have in mind 3.5 (I assume I can't use survival to help dodge monster's attacks, for example, although a literal reading might suggest otherwise). Backgrounds might be even better if the skills were framed more with reference to categories of experience and expertise within the fiction (eg "forester of the northern woods +3", or "cutpurse of the southern trading ports +3") rather than to abstract categories that only have meaning relative to prior editions of the game.
Anyway, that's both my interest in, and my views of the current limitations of, backgrounds.