I think they mean it's not designed to be able to converse with the user over long/complex topics, but it can generate fictional conversations fine.

Not necessarily. Where do you think the overlap is between these two tasks?

Good question! The overlap is a very interesting space.

Perhaps the overlap is where human input and oversight becomes valuable: in terms of veracity, trust, relevance, interestingness, etc

Yeah, I guess "creative writing" in this case is a shortcut for essentially saying they aren't that good at conforming to user-specified constraints. They can generate "creative" texts but can't necessarily constrain and iterate on their output in a conversational setting effectively.