They haven't lost their original meaning of "female/feminine", though (e.g. it's not like the term "bastard", that now is basically completely unrelated to its original meaning, when used as an insult). It's insulting to call a man a "girl" or other synonyms for "girl", and the only reason for which it is is sexism. It's also the same reason for which some people are homophobic - they can't stand the idea of men being "feminine". When people are homophobic towards lesbians, it's generally because they can't stand the idea that a woman would not be attracted to men, the "center of the universe". The most common questions that lesbian women get asked by straight people are "don't you need a man in your life?" "how can you have sex without a man?" "what did men do to you to make you become a lesbian", and so on. As kids, it's ok for a girl to dress like a boy and play with "boy's toys", but the opposite is generally frowned upon and from a very young age boys are shamed and made fun of if they show "feminine" traits. The list goes on and on.
If he had asked "Why does this woman do this?", he would have gotten replies that said "We cannot possibly know why (because we don't know her), but maybe it's because...". Which is what (I think) he wanted. There was no need to use that phrasing. It was an honest mistake, it's all good.I don't think it's pointless or harmful to try to draw a corollary with another's experience in order to gain insight into your own. To take another's word as gospel wouldn't be smart, but then again, that's why he didn't ask "why did this girl do this?". He knew that nobody could know what she was thinking so he tried to aggregate other stories and take a stab at why.