The workers at the Riften Fishery go through the Black-Briar Meadery instead of using the main door down to the docks on the west side of Riften (directly to the left of the meadery). Given that it takes much less time, it would make a lot more sense for them to use the main door instead of winding their way through the meadery.
I can't recall if issues like this can be addressed in some way by adding or modifying navmeshes or if the "supposed" shortest route is calculated solely at the engine level.