Disagree. Currency exists because humans cooperate on a common medium of transaction. If cooperation didn't exist (via fiction), then the equilibrium wouldn't exist.
The author seems to not understand that there are reasons beyond untruth that can make this situation possible. crazygringo reply to my comment gives a specific example of this gap in the author's knowledge.
> ...conventions such as the dollar?
> Such conventions, however, are not clearly distinct from fiction...
Not clearly distinct seems kind of ok. While you might have dollars in a completely rational society in practice people have funny ideas about currencies especially when you get on to the crypto ones.
Our civilization idolizes the human expert, like they were possession of some magical unquestionable truth. But to general human interaction, no such truths are available. To the mass of humanity, all they have is their experience of the world, and belief in the foundational institutions of their culture.
One such institution is belief to a better tomorrow, and that it's worthwhile to improve oneself. I think it is a wonderful institution - but image of the self or the child in the future, educated and improved, is whisful fiction until it becomes actualized through years of work - or does not become actualized if tragedy, trauma or change of life's priorities occurs.
We are not creatures of knowledge. We are a creatures of fiction. Some of us can grasp at - perhaps glimpses - of true knowledge in the strict mathematical sense - but that is a rare and wonderful aberration to typical way humans live.