From what I've read on various disasters, this seems to be true. By and large, people tend to be helpful during disasters.

However, one does have to keep in mind that, just because something is the norm, doesn't mean it's always guaranteed. There are also well documented instances of people taking advantage of disaster scenarios. There are also those who, essentially, do nothing. Neither contribute nor take advantage. They just remain in a shocked state.

There's an old military saying that goes something like, "Be polite, be professional, but have a plan to kill everyone you meet."

While that's kind of extreme, it makes a lot of sense. Even if people appear to be friendly, you should never put yourself in a position to be taken advantage of. Vigilance and Preparedness go hand in hand.