I usually think of the line between in-universe meta and fic as having to do with whether the thing itself could be produced using only the knowledge available to a character or characters in the universe. Things that use an omniscient third person narrator are much more likely to be fic than meta, things that show their authorship and where there isn't omniscience tend toward meta over fic. It's not a perfect rule, but it does pretty well for big bucket sorting.