This is not so obvious. This is one of the possible points of view, of course.
"He had tons of proof of that"
For example? I'm not sure other countries stamp a reason for entry like the US, it's usually an entry stamp for anything and that's it.
I'm also sympathetic to the author, but he was extremely naive. The border control doesn't want to hear about nice food or nice wildlife or other blah blah blah. Direct and cooled down answers will do. "On Vacation" is fine.
It's clear his answers (and passport stamps) rang a ton of bells.
This is a horrible way to greet people to come visit and spend money in your country.
My experiences traveling abroad are that most of the other countries have agents that don't make you feel like you are a burden or threat. Imagine actually feeling welcomed when you visit a lush vacation spot.
Depending on the details, yes, it's better, like, "oh, I transited through Malaysia when leaving Singapore"
But remember "anything you say can and will be used against you", so don't go into details unless needed.
And to be honest, someone saying they traveled there because of the Botany, they're either a plant expert or this can be felt as they're hiding something.
Sorry, but it sounds like this guy is a bit of an idiot who didn't help his case, even if the border patrol was overly critical. Trust me, I'm no fan of the TSA or their "SPOT" nonsense, but if I said the things he said, I would expect to get denied just out of spite.
You don't talk to police like you talk to a friend -- you keep the scope of the conversation limited to the question asked. You don't introduce the topic of Al-Qaeda. You don't go into political/religous discussions. Once you do that, you're putting the border agent/cop in a position where he needs to apply subjective judgement. You avoid that by not inserting unrelated noise into the conversation.
This isn't a US issue -- it's a clueless person issue.
It's an issue everywhere there are cops and politics. Every country has some goofy immigration thing to deal with. If you travel the world and are ignorant of the countries you visit, you'll run into trouble.
For example: Canada is probably one of the most chilled-out countries in the world. Nice place, friendly people, no kafka-factor -- Unless you're travelling with a party of people, and somebody was convicted of DWI a decade ago. That individual cannot enter Canada without a visa. Kind of sucks when you're in a car trying to cross one of the smaller St. Lawrence river crossings -- you're stuck in the middle of nowhere.