Good question. I’ve never heard the term before. As I read the article, I would take a stab at this definition. Old fashioned socialism is something that politicians and assorted pressure groups actively lead nations into, whereas postmodern socialism is something they kind of fall into, by a combination of mental laziness, cowardice, good intentions, denial and rank innumeracy.
Postmodernism essentially means that reality is created thru the use of words.