Why would a story teller need to know about abrogation? What is the context that made Aly (RA) ask him in the first place about such knowledge, then chastise him for it?
I think that when they say "story teller" (قاص), they meant one who told stories of the Prophet, PBUH, (Seera) and his fellows (Sahaaba). That involved many hadeeths.
Just realized that this explanation is very important. If he was telling hadiths, then he should know the abrogated and abrogating since the abrogated hadiths are no longer valid. Is there a reference we can cite for this characterization of قاص?