Exactly -- the Sokal paper makes the claim that since the paper was obviously nonsense, the incident proves that the 'vaunted academia' is off their rockers. But this is hinged on the assumption that the meaning of the text is derived from the intention of the author, and since the author intended it to be nonsense then the paper must be nonsense. But this is hardly something that we can assert unequivocally. The question of where the meaning of a text comes from is exactly one of the thorny questions that 'postmodernism' aims to address (among other disciplines).
One could claim that having read enough post-modernist work to be able to successfully emulate it, he had in fact become able to coherently express ideas which he could then also look at and proclaim to be nonsense.
Alternatively, given Sokal's own description of the paper as "a pastiche of left-wing cant, fawning references, grandiose quotations, and outright nonsense . . . structured around the silliest quotations [by postmodernist academics he] could find about mathematics and physics", one could argue that Sokal was merely repeating back ideas which post-modernists had already espoused, which leaves their resulting publication of his "nonsense" rather unsurprising.
