Universal grammar only speaks to the ability to parse and form sentences, not to internal logic.

That ChatGPT is capable of producing human-like sentences from pattern recognition without any universal grammar baked in, even if the underlying reasoning might be flawed, goes against the argument of something such as universal grammar existing.

At the very least, it shows that a neural net is capable of parsing and producing coherent grammar without any assistance from universal grammar. It does not prove that humans don't have it, but it does make a compelling case that it's clearly not required for humans to have it either.