One could say "it's a joke", without explaining it, thus, not ruining it.
Also, saying some vague shit and then claiming it as a joke is very convenient.
Finally, police injustice is not a subject for humor. It's no laughing matter. I'm not the one who's not "getting it" here.
Highering is an existing, valid word, and it fits the phrase.
https://en.wiktionary.org/wiki/highering
I agree that it is an unusual choice, but that doesn't mean you can assume it was a mispelling.
Moreover, the meaning went through. Ultimately, the word itself does not matter, and none of your explanations are relevant.
The original poster said they were worried about this leading to "highering illiterate officers"
Mis-spelling the word 'hiring' as 'highering' when expressing a fear about falling literacy standards in the police is ironic, and therefore funny.
Further elaboration was not warranted, but I'm providing it as a public service.