The exact description was that during the warrior's final scenes, if the inquisitor in your group had completed his/her storyline, then he/she would appear
I'm skeptical to believe this, as when I ran the story with my friend, we ran a Warrior/Inquisitor duo. We completed his (warrior) class FIRST, then did mine (inquisitor) and I saw no cameo of his fairly noticeable character in the background. But there is an explanation for this I suppose, or perhaps he was on vacation.