No, to answer the question at hand your starting point IS the general population; you need to know what percentage of males and females have the ability and inclination to become software engineers (in this case inclination is probably the relevant factor; I assume for the sake of this argument that equal numbers of men and women have the required ability).  If the relative proportions of men and women who have the inclination to become software engineers matches the proportion who actually do become software engineers, that is evidence against the sexism hypothesis. If the relative proportions do not match, that is evidence (not necessarily proof) supporting the sexism hypothesis.