Is it really? I feel like it just takes a basic amount of curiosity to ask yourself: "Huh, is this really how it works?"
I'm optimistic about the general population asking those kinds of questions, but I might just be a(n elitist) technophile. :-/
Something my dad told me: Never be one misstep away from a big mistake.
Even if he did ask himself if it was actually private, he apparently didn't attempt to ensure he was right. That should be obvious to anyone. Who doesn't look over the shoulder before talking about a sensitive subject, even if you are alone in a public place?
I have an obsession about checking the door handle when using public bathrooms, which is why I hate the accessibility adapted door handles very common here in Sweden:
Bill Gates was apparently humbled when he went into a room to watch usability tests and saw a lady trying to use a mouse. She reached the end of the mouse pad, so she kept moving the mouse onto the rest of the desk surface, and then down the desk leg. It was humbling. Don't know if it's a true story, but can imagine it happening.
Never make assumptions about your users ability to think the way you do about your interface. That's unfortunately (and often unintentionally) arrogant and a recipe for disaster.
what's so surprising was that even after thousands of people started to follow them, they still didn't notice that it was a public conversation they were having...
I wonder if he owned up to the impropriety of using your official position to reimburse your mistress for things she bought for herself.