I don't really care about Karma on this site (mine or other people's). If I did I certainly would have checked this comment earlier ;)
If people post for Karma instead of for content, IMHO it is their problem. It won't make the site much better, but it won't make it much worse, either.
So shame on him? I don't know. Major props for being honest.
One could argue you were subconsciously influenced toward posting a shaming comment because of the karma incentive.
Of course, you may just be joking as well.
It's certainly funny either way.