I don't see what is supposed to be strange or novel about this result. The usual norm, at least in Western and not too distant societies, is that among people who are stuck together for whatever reason, food, drink, and smokes should be shared to some degree. (More specifically, you're supposed to offer to share if you're consuming in front of others or if someone asks politely, as long as it doesn't become exploitative, and even taking a reasonably small amount without asking is at worst a peccadillo and often tacitly agreed upon as OK.) Money, on the other hand, is sacrosanct and stealing it marks one as a thief altogether unfit for company of honest people. I don't see anything particularly irrational about these norms, and while it's hard to pinpoint their origin and rationale precisely and completely, there is no shortage of plausible hypotheses.

Interestingly, I apply similar principles even to panhandlers. I never give them money, but if I'm carrying bags full of booze, I'll give them a beer if they ask.