Like so many things that are said with rhetorical intent, this character assessment is made as though it's a black-or-white thing (i.e that one is either completely paranoid to the point of psychosis, or one is not paranoid at all). The truth is that everyone is paranoid to some degree, to the extent that everyone is wary about potential dangers in their environment. The opposite of paranoia is not robust mental health - it's naivete. A moderate amount of paranoia is adaptive.
And speaking of adaptive, it's appropriate for Assange to be more fearful of people's intent at this time, because people are actually out to get him. When you're in a position where failing to wear a condom gets you a one-way ticket to Gitmo, I'd say you're well advised to be hyper-vigilant.