Consider it from the perspective of a loan - if someone you don't know well asked you for a loan, and said it was secured against "cult-booblahs" and that they were meeting with another member who traded in "cult-booblahs" this afternoon to sort it all out, it probably isn't going to go too well. From security's perspective, they are going to be immediately thinking one of: some weird drug lingo/money laundering situation, some weird pyramid scheme, or some cultist or anarchist dealing in imaginary currency. You've just made a simple question far more difficult than it needs to be.
It kind of raises the questions - why would someone with only $600 cash in the world be entering a rather expensive country for two months? From security's point of view, why would someone with only $600 cash have thrice that or more invested in some weird investment scheme? Finally, how does the founder of a bitcoin exchange have so little liquid assets/accessible emergency credit?
As an FYI, the author mentions they're from the UK or Ireland, and we were asked the same questions in both places (ensuring you have enough funds to support yourself) upon entry so this isn't US specific. Bringing enough cash to support yourself is expected (you could have said you are collecting a $10,000 loan rather than bitcoin and you probably would have still been refused - visitors should be able to demonstrate they can support themselves for their trip without relying on some deal going through once they're in the country).
I hope travel insurance covered the cost of the unfortunate trip.