True, but there are specific attributes that constitute classes legally protected against discrimination. Race is one of them. Intelligence is not.

https://en.wikipedia.org/wiki/Protected_class

I am not a lawyer, but it sounds like Jordan attempted to argue that intelligence should be considered an additional protected class, like race or religion, but the courts disagreed. Since intelligence isn't a protected class, and since the discrimination was applied equally across all applicants, Jordan didn't have any cause for compensation from the police department.

Your hypothetical situation, screening for blackness, would absolutely not fly since color is a protected class.