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narrative piece composed of chit chatting and joking
Explanation: After the end of the commercial, the people on the cafe were immediately engaged in a seemingly "organized and collective" discussion of the commercial, in a joking manner. They looked like as if they are part of a narrative piece, with chit chatting and joking as its genre.
Explanation: from the context you put I got the feeling that this is what's meant but I'm pretty sure it's not a literal translation of the term. However I think it gives a sense to what is intended by it.