Sam Altman's bet isn't interesting in itself, as it looks today the market was significantly undervalued in 2015. Even Sam Altman's pretty aggressive estimations undervalued it, he just guessed wrong on which players would become big. So it definitely wasn't a bubble.

Definitely. If we get to wiggle things in retrospect, then we're not talking about the bet itself, but the set of all bets that 5 years later somebody on HN would see as plausible wiggling of the terms to match current conditions. That's surely a lot of bets, among which we'd expect to find several winners.