They are not convinced, simply worried. If you look at Nvidia, Microsoft, OpenAI, Oracle, etc that is sort of passing around 100B usd without it actually resulting in anything being produced, it becomes worrying. I don't think the author is convinced, simply worried.

Specifically, it is the act of "I will invest 100 Billion in you, you will use that money to buy 100 Billion worth of goods from me. Both our balances look good, none of us spent anything." As I understand it, this act isn't so uncommon in finances but never on this scale across this many companies.