It's hard to say. I know of several kids with Aspergers that had friends to hang out with- some of those friends, of course, were not good friends and I wouldn't let my kids hang around with them.
This is what made me think that maybe someone he thought was a friend asked him to go somewhere and meet them. He might have been thinking he was just going out for a little bit of harmless fun, but someone may have had evil intentions. As we all know from this website alone, no one is really safe anywhere- Aspergers or not. It's just harder for some folks with Aspergers, as they don't seem to develop that intuition until their adult years, that something might not be safe or a good idea to do.