It is because he doesn't want the person to believe that his subconscious is unhealthily infatuated with said unknown person. Never mind that human might appreciate the base reference or even the ancient happy memory that dredged them up into the recent dream. The shields are up because it might be interpreted as something Freudian. Something dangerous. A deep, writhing hatred? Who is kaiden protecting? Himself, the faceless friend? The readers, from the horror of the truth?