Nobody is capable of totally throwing off patriarchial brainwashing.
Girls/women are taught and shown that they are less important and boys/men that they are more important. And everyone is taught gender ideas i.e. what boys/girls, women/men are really like.
A boy growing up feeling female is still treated as a boy by those around him. Maybe an effeminate or non conforming boy, but a boy none the less.
Boys growing up in female dominant environments - first off all there is no guarantee that those women will still not impart patriarchial ideas or behaviour to the boy - even if they try really hard not to do so. My mum swears she treated my brother and I the same - she didn't. For example, at a really basic level, we both had chores - I was made to do mine, my brother was regularly let off his with feeble excuses.
Also parents are not by any means the only influence on children. School, peers, teachers, tv, toys, adverts, other adults, how they see society being organised e.g. who digs up the roads - all of this also teaches and influences children's ideas and behaviour.
If a society is based on the patriarchy, then yes boys will grow up with ideas and behaviour that supports this including sexist ideas.