Both postmodernism and modernism reject boundaries and rigid genre distinctions, emphasizing irony, parody, and playfulness. Postmodern art (and thought) favors reflexivity, fragmentation, ambiguity, and an emphasis on the destructured, dehumanized subject.
But postmodernism differs from modernism in its attitude toward a lot of these trends. Modernists uphold the idea that works of art can provide the unity, coherence, and meaning which has been lost in most of modern life; art will do what other human institutions fail to do. Postmodernism, on the other hand, doesn't lament the idea of fragmentation or incoherence, but rather celebrates that. "The world is meaningless? Let's not pretend that art can make meaning then, let's just play with nonsense."
for a bit more info along those lines)
In short, it embraces itself for what it is, not for some strange external validation. Nonsense as salvation is an excellent maxim for it. The problem is, though, that Postmodernismn (like many Pagans) never offers answers. It's a very annoying way to look at the world, in my opinion.
However, Pagans have constantly challenged scholars of religion, who like to look the other way because (in the words of one professor I querried), "It's dumb." (No, I'm not going to say who, to protect the identity).
Paganism doesn't fit in the neat boxes we religious studies people have created, so it makes us uncomfortable. That leads to us ignoring it, and assuming that it's a "dumb" thing that must not require any study classes it squarely in "postmodern".
Kinda roundabout, but that's how I see it :)