If the test is not susceptible to flukes, then my argument doesn't work. That said, flukes aren't necessarily extreme outliers. The red weasel you hired is more likely to be a slightly-below-standard performer that was having an unusually lucid day when you interviewed it.

On the other hand, Wei's argument works even if the test has no flukes. Here's one way to reformulate it: your binary decision to hire or reject a weasel is not informed by gradations of skill above the cutoff point. If blue weasels are more likely than red ones to hit the extreme high notes of software design (that weren't on the test because then the test would reject pretty much everyone), you'll see that inequality among the weasels you hire too.