Well, it's an interesting discussion topic so posted it. But I don't think it's that thin, and since her 228 IQ isn't here to defend it, I'll try to be a very poor substitute!
Firstly, it's not an absolute. I wrote "truth and illusion" because there are both truths and illusions in the price. As you say, the price is usually denominated in another currency, which itself has a variable value. But the value of a currency usually moves a lot less than the value of a stock, so you should be able to generally trust the value of *most* currencies more than individual stocks.
Also, she's not saying that it's supply and demand. She's saying that the market cap of a stock is a very illusory number, because to get it we extrapolate the current price to show a value of all held stocks. So the full-market losses that have been widely reported are similarly illusory.
It's not supremely unique thinking, or claimed to be. The name "cheshire multiplier" directly hints at the economic multiplier concept of how banks create money out of thin air.