All the human brain does is determine how to fire some motor neurons. No, it does not reason.

No, the human brain does not "understand" language. It just knows how to control the firing of neurons that control the vocal chords, in order to maximize an endocrine reward function that has evolved to maximize biological fitness.

I can speak about human brains the same way you speak about LLMs. I'm sure you can spot the problem in my conclusions: just because the human brain is "only" firing neurons, it does actually develop an understanding of the world. The same goes for LLMs and next-word prediction.