Maybe in part, although I think girls, more so than boys, also tend to be raised to care for others as well as express their own emotions, which would make them better at reading others' emotions too.
Girls certainly do seem to care more about appearing caring and compassionate than the average guy would want to (in contrast, a 'male' upbringing would tend to phrase pro-social norms in terms of things like fairness, a strong character and the inner pride of pursuing a virtuous life), but to imagine that they're more pro-social in general seems like a bit of a stretch! (I mean, it's not like girls can't be just as mean and spiteful to others when they have the inclination and opportunity to be.)
