Luhmann argues that society equals communication, not narratives, norms, shared memories, etc. Thus, according Luhmann, there has been no actual postmodern change because society still consists of communication. Postmodernism is a theory of culture; however, Luhmann displays little interest in culture. So it’s not that Luhmann refuted Lyotard, he simply wasn’t interested in the theory.
Social Systems Theory 