This is just stupid. There is no way in all hells he wouldn't know who gave him that cookie.
As I said before, even the most insecure guy in the world could tell WHO was responsible, and only WHY was still in question.
Heck, back in high school I got mercilessly teased for a while because one particular group of girls thought it would be hilarious to lead me on and give me the wrong idea. And while I never explicitly said anything, I almost believed for a while. It dealt a rather severe gut-punch to my ability to trust though.
I'm not even sure what kind of payoff they were expecting though. I was always a weirdo. If they intended to humiliate someone, wouldn't it have had more impact to pick someone who had a good reputation to begin with?