Literally the only thing you know here is that one department didn't like one candidate and came up with a reason to deny him based on cognitive overperformance. For all you know, they didn't like his hair color, and came up with an excuse. And that's it: out of over 15,000 police departments in the US, almost 1,000,000 sworn officers, and over 25 years, this is the evidence you have for the claim that there's an enshrined "right" to reject police officer candidates who are "too intelligent".

It's an Internet urban myth. I'm just stepping in to call it out as such.