It's possible you misunderstood me a bit. :) It isn't original fic just because the reader hasn't seen the show, of course. But from that reader's perspective, there is no familiarity with canon, character, setting, episode references, etc. The reader is entirely reliant on what the writer has presented in that story for her understanding of what's happening, and there can be, basically, no complaint of the story not following canon or characterization, because the reader has only the writer's own story to go by. In that sense, it's read as original fic - fic with no source foundation for that reader.

That fanfic is often structurally different from original fic is of course true, but beside my actual point. :)