Fear and paranoia are bosom buddies spawned from unfamiliarity. So, is Alexander too paranoid? You already answered that he is in a place that is almost entirely alien to him. It's a natural human set of reactions to be wary of the unfamiliar, to fear the unknown, to loathe what is obscured by darkness. You already mentioned that he is psychic, which is fine in a confined environment, but absolutely [i]mind bending[/i] (pun not intended) when suddenly thrust into a place with so many minds. 

In short, Alexander would be overwhelmed, distracted, and justifiably paranoid. I think you're doing fine; heck, I think you could make him even [i]more[/i] paranoid and off center. Within reasonable limits for the naivete of a child, of course