Understand that whoever controls the search engines controls the internet. Watch one search engine rule them all. The engine’s ranking algorithm is more secret than the Coca Cola formula. No one but the engineers who work on it know exactly how it works. The search engine is your reality interface—remember, you worship before the altar of the web and you’re just a back-of-a-head. But you don’t know how the reality is made.
Our reality is dictated by something we're not allowed to understand. The symbol here being that we are just a back-of-a-head. We have our heads down in our screens and we never lift them up to look around. The author is further illustrating our addiction by describing us by how the world sees us, as a back-of-a-head. Our reality is our addiction and search engines dictate it in a way we can't understand.