Great video and economic thought-exercise!
@andrarchy because you asked for input and thoughts, I will give my '2 cents' (see what I did there? ...poor economics humor).

Fiat currency can be anything and its value is strictly determined on what the market (community) agree it is worth. We could all switch from dollars to seashells if everyone agreed to. The value would vary due to a number of factors, including the total number of shells available in our economy. But the biggest factor of value is what the community believes them to be worth. If one day we decide to switch to green coconuts instead of seashell, then the value of shells goes down dramatically.

If you want proofs for your theories, then look at the evolution of money from commodity, to representative, to fiat. How each are used and the variance of relative value over time tells a compelling story.

During the period when commodity money ruled, a bag of rice was worth a bag of rice. Anything else would be negotiated based upon many different factors. You may get 3 chickens for your bag from one person while, the next may only give you a basket of eggs.

Representative money was fixed by a central and controlled structure. A bank, merchant, or government would provide a coin, paper, or some ‘proof’ that was redeemable for one bag of rice and only that. You could offer your ‘proof’ as part of a barter and the holder could redeem it for exactly one bag of rice.

The rise of fiat money changed everything. Create a token like the dollar bill and if everyone agreed it was the primary currency, accepted for trade, the system works. It is all based upon the cumulative negotiated power of what the token is worth at any given moment. It may be worth 3 chickens. But if the majority of people think it is only worth 2 chickens, then people only accept it at that value point. The buying power determines the value. Buying power is determined by buyers and sellers at any given moment.

That is how I understand it, at the Econ 101 level.