Fair point. Though I'd say it could be both! Mostly because of how disbelieving they all look at his sudden appearance. It even shows Fluttershy looking between the two of them and Twilight pointing over at them while looking pretty stunned.I think if they came right out and mentioned the whole AJ similarity thing, it might have been a bit too on the nose/not a suitable comment for Fluttershy to make at that time, since the "is that how romance sounds?" line was just a quick jokey comment that allowed them to move on to the next scene right away.