I think the next paragraph is a bit more accurate:

Postmodernism postulates that many, if not all, apparent realities are only social constructs and are therefore subject to change. It claims that there is no absolute truth and that the way people perceive the world is subjective and emphasises the role of language, power relations, and motivations in the formation of ideas and beliefs. In particular it attacks the use of sharp binary classifications such as male versus female, straight versus gay, white versus black, and imperial versus colonial; it holds realities to be plural and relative, and to be dependent on who the interested parties are and the nature of these interests. Postmodernist approaches therefore often consider the ways in which social dynamics, such as power and hierarchy, affect human conceptualizations of the world to have important effects on the way knowledge is constructed and used. Postmodernist thought often emphasizes constructivism, idealism, pluralism, relativism, and scepticism in its approaches to knowledge and understanding.

The key point of political theory post-modernist is that certain social norms are claimed to be true or universal when that is not the case. Further, binary distinctions (black/white, capitalist/proletariat) are inherently misleading, organizing the world in particular ways in order to advance particular moral agendas.