In any normal market, I think he is correct about the over-valuations. However, one factor that he didn't mention, is that the worlds two largest economies are in direct competition for global AI dominance. AI itself is seen as a technology that has strategic importance. That may tip the scales in favour of this situation continuing for some time. It's not just 'investors' confidence supporting those valuations, but in some respects, the strategic goals of major countries; neither can afford to lose this race. AI is somewhat unique in this respect, as compared to, say, internet pet shops in the dot-com boom.
OTOH, as he pointed out, there have been some large stock price falls just this week. According to yahoo finance, Alphabet lost half a trillion dollars on thursday
https://finance.yahoo.com/markets/stocks/articles/alphabet-just-lost-500-billion-203300362.html , which sounds like a lot of money to me, and several others have also lost large amounts. That doesn't sound like stability. Perhaps the recent rise in interest rates he alluded to will bring about a correction. We shall have to wait and see what happens.