I think the point being made is that there are probably predictors which have many orders of magnitude more predictive power (e.g. work experience, education, interview questions, programming exercise, available source code, etc.).

The male gender is probably correlated to programming ability as well due to the fact that there are more male programmers but it's not a very useful predictor.

> A high correlation corresponds to predictive power...

That's a bold statement. And one that is unfortunately often times false. Spurious correlations pop up everywhere. They can be notoriously bad at predicting things, and care must be taken not to take rash actions based on correlations that may have no actual clout. I'd say denying someone a job based off of an algebra test is sufficiently rash.