Keep in mind ChatGPT is a language model. It's designed specifically to simulate sounding like a human. It does that... Okay. It doesn't understand the information or concepts it is using. It just sounds like it does. It can't reliably do basic maths and doesn't try or need to. It just needs to talk about it in a believably conversational way.
The brain does far more than process information. And ChatGPT doesn't even really do that.