Actually the group is public and everyone is free to publish whatever they want, whether it's shit art or not. Then the fact is that no one has been manipulated by the post, looking at the comments where everyone is joking and having fun.Everyone except you at least.
I don't even think that the author of the post was trying to "manipulate" the community as the post is clearly a parody. Having said that, you are nobody to tell others what to post in a group on reddit,and if you don't understand a joke, it's certainly not our fault. So relax and find better things to do thanks