I think it is a joke on the "there are only 5 story types" blather you hear, every so often.
+ Someone goes on a journey.
+ A stranger comes to town.
Stories are attached to particular protagonists, but you can do things like overlap the stories of multiple protagonists or give a single protagonist multiple overlapping stories in order to develop narratives of arbitrary complexity.
One type, yes, and Kishōtenketsu as well. And now you know.