People wasting thousands without realizing it through gambling mechanisms? Absolutely.
But millions? I really doubt it. It's probably a buy / trade / sell money-laundering type of operation, and that player was pissed they lost some of their assets.
I guess you're not familar with streaming culture, nor you live in an Asian country. Bragging on how much you spend on games and streaming the process is a thing. There was a Taiwan streamer who spent about 100k in hours on stream.
Of course it can be all staged. But the culture is there, and it's not that hard to imagine some people who has more money than they can spend in a lifetime doing this just to show that they can outspend the streamers.
Westerners are into that too now, I won't name names but they're happy to do it because they consider it a business expense (a tax deduction so not free, but after you add the views and subs and donations, and sometimes sponsorships, worth it). I think the influence they wield in normalising their spending habits is a problem - some say to not do what they do, but it's all a very exciting process for people and I'm sure plenty of viewers say something like "yeah spending $20,000 is stupid, I'll only spend $500".
Reminds me of how I heard Vietnam is one of the biggest consumers of black market rhinoceros horn. Lots of people are making money there, but there are only so many legitimate ways to flaunt your wealth in that system.
But millions? I really doubt it. It's probably a buy / trade / sell money-laundering type of operation, and that player was pissed they lost some of their assets.