Don't focus on the female friend, it was just a word used as an example to show that son (meaning 'his' as well) can also refer to a female word if that one starts with a vowel.

The word friend comes from 'amie' which they merely used as an example to show I'm wrong. Nothing about a friend is actually in the French text.

And son can still refer to male as well, we just don't know yet.