I'm puzzled by your comment. Do our brains not exist in the real world?

I think he means that the brain does exist, but that our brains don't have a perfect model of the real world or physics, hence our dreams look like this.

Also, in a way, comparing GenAI/LLMs to how our brain neural nets work (which isn't exact, but have similar outputs).

When we are awake, we see with our eyes the ground truth.

When we are asleep, our eyes are closed.