I think what he means is that you simulate the brain on a deeper layer if you don't know how it works.
The process that requires the least amount of processing power but the most amount of knowledge is a direct approach where you encode the behavior of a human brain directly.
next up you simulate neurons neuron by neuron and their interactions.
Then one layer deeper you simulate all chemicals involved.
one layer deeper you simulate all atoms involved
one layer deeper you simulate quantum mechanics and all interactions that together constitute a biological brain.
All of these approaches cost more and more processing power but less and less understanding of the human brain. So if you had unlimited processing power you COULD simulate a human brain simply by simulating the absolute fundamental physical reactions in the system that will eventually produce thought.