ChatGPT was trained on, essentially, everything on the Internet... if ChatGPT has a "bias", then, no, it doesn't: humanity does.
Or in the accidental choice of source material no?
You're relying on a particularly unhelpful and narrow definition of "bias". There are tons of valid and widely-accepted uses of the word to apply ot unintentional bias and to apply to things incapable of having intentions.
They did do it on the purpose—the RLHF. The RLHF process was definitely biased, deliberately or unconsciously, in favour of certain political, social and philosophical positions (apparently the same ones held by many in Silicon valley/OpenAI teams responsible for this).
An expression which is only said by those with a liberal bias.