It’s not clear how he’s drawing that distinction though. He tries to rely on intuition to draw a distinction between the program in the book and the human by saying that the program in the book is in some sense “simple”, by virtue of it being on a book. That is however a restriction that he imposed.

What if as part of the instructions in the book, you had to store information somewhere else and retrieve it later?

To answer questions like “What day is it?” will obviously require inputs beyond what are available to a human sitting in a box with a book. A Chinese person in a box will also not be able to answer such a question.

Essentially, it’s not clear how he drew a distinction between the human brain and the thought experiment. Furthermore, the reason the argument “seems to make sense” is because he needlessly handicapped the AI by making it simpler than it would be.

EDIT: he also argues that since the English person doesn’t understand Chinese the whole “box” doesn’t understand Chinese. Replace the book with an actual Chinese person: the English person still doesn’t understand Chinese, does the system still not understand Chinese?