Or they didn't believe it was as good as cash, which is kind of a fair assessment. The guy he was going to meet might not have had the cash after all, and without a buyer, the Bitcoins have no intrinsic value. Saying that you have a suitcase full of collectable pins that you intend to trade with a guy for $1500 would probably not get you into the US either.
If you really had pins for trade, you'd have to declare them on the customs form (you'd be importing them), and selling them would likely count as commerce not valid for a tourist visa.
You can only get a visa waiver if you fall within the requirements of a tourist visa, plus additional restrictions. And visa waiver entry still requires that you fill out a customs form.
If you are carrying more than $10,000 worth of securities or cash, you have to declare that. But there's absolutely nothing wrong with owning more than $10,000 worth of securities and liquidating them while you're visiting the US.
Here's the official government documentation on the matter:
What if you have US$10,000 in your bitcoin wallet on your laptop? Is that the same as US$10,000 worth of collectable pins in your suitcase, or the same as US$10,000 worth of code/IP on your laptop (which I can't imagine anyone declaring in customs)?
Then it's the same as any other asset you have access to but isn't liquid, so it's not an interesting question when you're talking about how much you can take through customs without declaring it.
