Yes, I agree. That's why making it a girl is so hilarious. As to why you're so offended that I find it hilarious, I honestly don't know what to tell you. It's funny for the same reason I'll refer to a hypothetical serial killer as "him" and follow by saying "or her, of course" to females as if I'm pandering. The joke is that they weren't offended to be excluded from being serial killers.
And I'm not offended. I just have zero idea what your issue is. I never gave it any second thought what gender the person is. I don't care and I wonder what you're reading into it.
On a serious note: What are you on about?