[__MatrixMan__]

The question in the article title sounds to me like:

> Why are people from the USA bad at navigating the New York subway?

And you're right to point out:

> People from New York aren't.

If people are surprised by the idea that many mathematicians are bad at arithmetic, then I'm guessing they also think that arithmetic is taught first because it's fundamentally foundational, rather than something to do with Diophantus having lived before Erdős.