Run the same thought experiment the other direction: at a low level, the human brain is just physics and chemical mechanisms, which in principle could be perfectly imitated by transistors calculating the same output. (Yes, such a thing isn't realistic, but neither is billions of humans doing perfect matrix math by hand.)

I still haven't seen a robust definition of "intelligence" that would allow me to tell the difference. (Bear in mind, this is a definitional struggle even in biology: if we were walk back the evolutionary chain from a human, to a protozoan, it's not clear that you could pick a single point where a non-intelligent creature gave birth to an intelligent one. It's a Paradox of the Heap.)