Is there a syndrome or other diagnostic for this type of behavior? When poking about as to what Chris McCandless was thinking, I found repeated references to a "Schizoid personalty".
Schizoid personality disorder (SPD) is "characterized by a lack of interest in social relationships, a tendency towards a solitary lifestyle, secretiveness, emotional coldness, and sometimes (sexual) apathy." I got that from
http://en.wikipedia.org/wiki/Schizoid_personality_disorder .
There are certainly people who live by themselves in isolation without being grossly unprepared and accidentally doing themselves in. Someone with SPD would be more likely to not have told anyone what he was up to. The article didn't say as much, but I get the idea that he was excited about it.
It's hard to diagnose someone's mental condition from a news article, and I'm not a mental health professional. But it doesn't seem to me that he suffered SPD.