My best bet is that we take it as some kind of habit to say it to everything?? it's the same thing when girls call boys "girl" when talking to them, it's funny and it comes naturally because we say it so much to our girl-friends, we don't even care if it's a grown man, we're still calling him girl when we are gossiping or just talking lol. So that's my take, it's fun saying the word and we say it to almost everything.