He might be contractually obligated to do a certain number of them for Marvel. As far as him having issues with fan contact and crowds, he’s just finished with a long desensitizing experience by doing his Lobby Hero stage doors, so I can’t imagine that he’d have as much of a problem with anxiety with that for now. It just doesn’t seem to me that it would be a big reason for canceling the event.
I’m inclined to believe what he said: it was an unforeseen family matter. Whatever that means. It just doesn’t seem like he simply wants to spend time with his family (the comic con was only a weekend, anyway), but something came up with his family that prompted him to cancel.