So the Cullen and shortbread cookies thing has a whole history in the thread too, and it's not hard to imagine that it's one of those little details that Brienne threw in as a nod/tiny shoutout to the fans that kept Cullen's thread going for years and years, playing a big part in turning this minor side character into such a major player. Who even knows how the Cullen + shortbread cookies stuff got started anymore, but it's one of those things that's too coincidental to be a coincidence, that an ancient little inside joke in Cullen's fandom would end up becoming canon once he got a bit more personal writing. 
It started because the writers of followers apparently always (or at least for DAO and DAI, not sure I've ever seen them for DA2) decide what their characters would be if they were food, and at least for DAI they teased people waiting for the release of follower names, pictures, etc. by naming 12* foods but (mostly) not saying who was what. Shortbread was one of them, and as far as I know this page was the first time it came up in connection to Cullen.** BioFan later ran with it by using it in photomanips to welcome people to the thread.
I think dialogue probably would have been finalized by then, but it's a small enough line that I guess it could have happened as a last-minute edit. I wouldn't bet on it myself, but that's partially because I like the idea of Josie's gift being butter toffee better. The lack of flour has always bothered me if she's talking about shortbread.
I've been itching to ask Brianne on twitter if that really was him. We didn't want to do it at the time because people were asking about the foods too much / reading too much into the ones they did discuss, and writers were getting annoyed. (In retrospect, I bet the meatballs or wax fruit were Blackwall, and no one would have wanted to know that early.) Still seems like the best one to me, though the strawberry parfait has potential too. (Actually, in retrospect... that or the bananas foster has to have been Josie. Doubling down on the shortbread guess.)
* Or something in that neighborhood, anyway; it was 10 at first, and I think it ended up 12+ eventually. But it might have been just companions; I think I remember Patrick saying IB was both the rump roast and the chili dog.
** In connection to Cullen and the Writers' Pit Food Meme, anyway. There's at least one older fanfic where he likes it.
Sorry for all the edits! I keep remembering things and coming back to this while my code is compiling.