Censorship only applies to the government prohibiting the people frm saying certain things
CC's right to air or not air what they choose to, or not to, is their protected free-speech right as much as Parker and Stone have the right to create cartoons that say what they want to say.
Just as our own Bob Hubbard has a free-speech right not to have these forums used as advertising for any Crackpot-McDojo-Soke-Ninja-Master who wants to sell his top secret fighting techniques, Comedy Central has a free-speech right not to show South Park if they don't want to.
Make no mistake, South Park is an enterprise, like Comedy Central. This is not about two little guys trying to stand up to the big bad corporation that wants to censor their free-speech rights. This is simply about two private enterprises, both of whom enjoy free-speech rights, in a conflict because one of the wants to sell their stuff and the other one doesn't want to be the one showing the stuff to sell. When it gets down to it, it's just a contract dispute over what sort of obligation and/or editorial control Comedy Central has over South Park episodes