Other factors that could explain:

The difference is not as large, either because of the file drawer effect, or because someone selected / massaged the data to make the difference look bigger (the researcher or the journalist).

Selection effects: men and women may go into economics for different reasons; for example (as a bit of a caricature); men who want to get obscenely rich study economics to get into business, and women who want to get obscenely rich try to marry into money, and money-grabiness is correlated with pro-free market views.

Differences in peer groups: there seem to be more men than women majoring in economics, so assuming one's views are influenced by peers of the same sex, it seems likely female students will have more non-economist peers.

Differences in conformity: women may conform a bit more to widespread social views (at least, to views of "their social class") and/or compartimentalize more between what they learn about a specific topic and their general views. This would mean female scientists would be slightly less likely to be atheists in religious countries, female theology students would be slightly less likely to be fanatics in not-that-fanatical societies, etc.

Changes in major: I don't know how frequent changes of major are, but if they are frequent it seems likely you'd see more women than men coming from social sciences in economics (and more men coming from mathematics).

Different subfields in economics: Maybe "economics" shouldn't be considered one big blob - there may be some subfields that have more in common with other social sciences (and thus have a more female student body, and a more "liberal" outlook), and some more in common with maths and business.