Is it normal for women to use male pronouns by default?

Usually, if I don't know the sex of a person, I'll default to calling them 'he' and 'him'. While it is a little bit sexist to assume it's always a male, I never really cared since I always thought that men just assume it's a male because they're males. And that women would assume it's a female because they're females, and so they'd use 'she' and 'her'. So I thought people just default to using their own sex's pronouns for the person. However then I realised that my mum and sister always use male pronouns as well when they don't know the sex of the person. Is that normal?