[bemusedthrow75]

It's not unclearly specified. It's very tight.

People who get it wrong are usually projecting some implied understanding onto it, which is why they get it wrong.

Which is the point of the problem. It's designed to reveal this tendency in analytical thinking leading to unexpected outcomes. You get it wrong, you're gobsmacked, you understand why, you gain some enlightenment from it. It's fun to be wrong in ways you later understand. (This is one of the thrills of programming: that moment during debugging when you shriek with joy: "YES, IT BROKE!")

The fact that it also exposes the way some overly confident people lash out with anger that exposes other biases is the point of the article, I think.

[nickpsecurity]

I could see that. Both that it could be the intention of the problem statement and what you say it achieves. It had that effect on me.