Considering religious citizens believe in the writings of books that "command" believers to help others this finding is hardly surprising. Saying that such people are "nicer" though is too simplistic. Moreover, a fellow soldier who does not believe is just as likely to take a risk to save you in a battle as a religious person.
Atheists also give less to charity. Considering most charities are religious institutions, this is to be expected as well. Is the behavior of believers really altruistic? They are trying to get into heaven after all. Belief is a fickle thing. Even atheists have faith. They have faith that God does not exist.