Injust actually is an archaic word (with the same meaning as unjust). However, it's equally likely in this case that the person knew this as it is that they are illiterate.
Even funnier is that evildoer is a word, so it's hyphenated (as you point out) for no reason in this case.

Is this real?
please say sike
Edit: the headline is fake, but it's a real article.