I think you have to pull your question apart in to two implications of "truth". There is a "ground truth" question (from plato's shadows on through today) which is not addressed in this essay.
But there's an epistemological enquiry that is at least as important, which is into the validity of our internal states and reasoning/justifications. Search down to the discussion starting with "We are, when philosophizing about experience and its objects, mesmerized by the analogy between having a chattel and having an experience." The author is referring to the deep analogies we quickly use to reason about things and how they can immediately lead us astray, often irrecoverably.
This problem is made worse by the internal private languages we each develop: I generate my utterances in the desire to induce some mental state within you; you respond similarly. What model and process do I use to convince myself that I have adequately induced that state in you? That's also an important sense of "truth"