I don't know about legal requirements, but I'd bet anything their training doesn't tell them to just say "have a nice day" when someone refuses to answer simple questions.Then it should. He is under no legal obligation to answer their questions. If I were to try something similar, I'd be much more polite about it, but, rude or not, he was perfectly within his rights to refuse to answer.
Now, if other factors were enough to actually raise reasonable suspicion that he had done something wrong (such as smuggling some contraband into the country), then the proper response is to move him on to further screening.
It's unreasonable to treat them as goons for simply doing their job.
Ah, yes, the tried-and-true "just doing their job" argument. I don't buy it. People are responsible for their conduct while performing their job. Their employer may set policy, but in the end the person implementing that policy that must accept shared responsibility for that policy.
They're real people, most of them probably decent ones (because really, most people are decent people)
Wait, wait, wait. Now, I'm going on just the words of the author here, but:
"The officer changed tack to bad cop. 'Let this guy sit until he cools down,' the officer loudly said to a colleague. 'It could be two, three, four hours. He’s gonna sit there until he cools down.'"
How does that describe the actions of a decent person? I don't care if the author was rude to the customs official. Declaring in a power-trip manner that you're going to make someone wait for 2-4 hours just because you can... how is that decent?
I do think the guy was a bit of a douche in how he handled the situation: "none of your business" is probably one of the rudest ways he could refuse to answer. Something more like, "I'm sorry, but I'm not legally required to answer your questions and would prefer not to," seems like it would have garnered a better response, both from the customs officials, and from the hordes of commenters calling him a douche. If he had done that, and still was subjected to the same mistreatment, I'd feel a lot more sympathetic. But still, he did nothing legally wrong, and exercised his rights as a US citizen, and was detained and hassled for it. That's wrong.