It is clear the author has not read any Derrida or Foucault. Or any other postmodern primary texts.
Nor have you.
Tell me: how have I misunderstood it?
Postmodernists are often accused of saying things they never said at all.
In my response, I offered one example: Trump supporters who believe there is no basis for proof of truth (except for the claims of a despot) are doing what they falsely accuse postmodernism of doing.