It's like there are at least two layers of funny money accounting going on here.
First, you have the strange way that people equate market cap with value. There's no guarantee that holding shares with a current market value of $X will eventually return $X or more in dividend payments plus maybe some eventual disposal of assets, and these are usually the only tangible values involved. A market cap based on ludicrously high P/E ratio will be high, but trading those shares is like trading Bitcoin: it starts to look more like a Ponzi scheme than a genuine value-based investment.
Second, even the market cap is mostly theoretical here, because any shares held can't be freely traded on an open market. The asset is almost completely illiquid other than occasional anomalies like the secondary sale we're talking about. The first IPO of an AI unicorn could be the pin that bursts the bubble.
It's the difference between being one of the AI unicorns that doesn't actually make any real profit yet and is largely funded based on hype and hope, and being a supplier like Nvidia that is actually being paid real money (funded by all the AI investment) and has a P/E ratio that is high but not off-the-charts stupid.