Is the river the flow and the boats the user stories?

Well, during the Kanban Coaching Exchange Meetup today, Tom Sedge shared this thought “The river is the flow and the boats are the user stories”.
In my opinion I agree whit this since smaller user stories are faster to understand, implement and deliver by the team.
This also means that, big user stories are like big boats that can have hidden complexity, are harder to implement and can become the bottleneck for the flow/sprint that is been played by the team.

What do you think about this?