It doesn't change the main point, which is that the value of the stock market is derived from the value of the actual companies. It doesn't matter where the money is coming from to buy those stocks.
By the real profits of the companies in question according to standard accounting rules.
It's not "perceived value" or "demand" or anything else that can be affected by speculation or hype. It's literally the units of money produced by the company that issued the stock.
Buffet's rule of thumb says that ultimately the value matters. Investors and banks can play whatever games they like trading securities, building new financial instruments, speculation, etc, but ultimately the value of stocks is tied to the amount of money produced as profit, and eventually the market corrects.
So far he's been right.