I think there's a bit more to the background mental framework. Postmodernism (as best I understand it) says that all truth claims aren't actually about truth. Those who believe such things need not concern themselves with whether the facts support their position. So far I'm restating what you said.

But postmodernism says more. It says that truth claims aren't actually about truth, but are assertions of power. Those who believe such things are likely to have that intent when they write. Keep that in mind when you evaluate what they say.