I don't doubt this but got any good references?
The reality is that the cash flow and assets underlying these securities were overpriced. In spite of it, institutional investors speculated the price up for years. People thought they had found a way to "cheat" risk, turning fundamentally risky (and therefore, low-value) assets into something more valuable. They were wrong!
Other times, the market is simply too optimistic (dot-com bubble), and attaches large valuations to companies with non-existent cash flows (i.e. little fundamental value). We're arguably in a similar current today, although it's not nearly as bad, imo. The companies that get overblown valuations today at least have revenue, albeit some more legitimately than others (TSLA vs UBER).
Speculators control all of the short term movements (everything on a time scale of <1 year). Sometimes when new financial instruments (what value investors would call fads) are created, they can control it for years (securitized junk bonds, in the 80s, sub prime mortgages in the 2000s).
But the pricing of securities in the market has always regressed to fundamentals in the long arc of history.
The value investor types agree with the nasdaq guy, though. All institutional investors (even the pension fund managers!) behave like speculators, since at least the 80s. It’s just how the incentives are structured.
It’s important to understand how they think, because you don’t want to be trampled by them. But playing their game is not the way to win in the long term.