In practice this is just Goodhart's law itself. It's not distinct. In Goodhart's law

> when a measure becomes a target, it ceases to be a good measure

If you ask someone "could you give me an example" you will see that in the example the measure that becomes a target is already a proxy. Even the example that the author presents, the good that cares a lot about testing its students... How does the school test its students? With exams. But that's already a proxy for testing students knowledge...

But overall excellent article.