I think this is conflating factual and rational. They are not mutually inclusive.

Although its a book on economics, Von Mesis's "Human Action" premise is that all human activity is necessarily 'rational' from the viewpoint of the actor. Moreover, the goal of "human activity" in general is to bring about a higher state of happiness. Even the refusal to perform an action, is in effect an 'action' who's goal is to increase happiness compared to the alternative.

A person who is convinced they are being hunted by aliens, so wraps their head in aluminum foil is behaving completely rational from their view (by increasing their happiness of not being tortured)...whether or not this is factual is a different issue.

Are you really in a position to declare that that was not the case? Do you posses all evidence, or is there actually a chance that there are things about the situation that you don’t know?

Also he was mentally ill, his brain worked differently than normal. Rationality depends on perspective. He was probably acting with rationale according to his experiences.