I don't think it's too much to expect cops not to deliberately abuse their power. You don't need to be Wile E Coyote, Super Genius to know that is wrong, and when a cop says, or thinks to himself, "I'll just make stuff up" then there is no question that is what they are doing - no "ignorance of the law" applies.
That cop should go to jail, IMO, for deliberate abuse of power. If you can't trust a cop not to "make stuff up" over a nuisance, imagine what he'll do when there is real crime. I wonder how much stuff he has made up in the past? All of his past and future court testimony should be considered in the light of what he just said he'd do to get the result he wanted.