My cynical side thinks that Joss wants to pique our interest in Fray so we'll all rush out and buy the paperback so we can work out what the hell is going on.

And this is me, thinking: Well, Joss really handled it well to give all important Fray-information to the reader so they don't have to grab the Fray-paperback in case they don't want.
On the other hand, I *know* the Fray-Story and therefore could follow quite easily.