alt Hacker NewsI think what he means as music theory is the next step after what this (blatantly AI-written, but passable) article talks about. This is the part that you take for granted, but it certainly is music theory in the same way that Peano's axioms are number theory even though you don't use them explicitly.
There's no such thing as "music theory".
Music theory was originally a tool for music critics in the 19th century to talk about conservatory music of the time.
There's nothing rigorous, systematic or scientific in it; it's mostly a historical cultural artifact more than anything else.
For example, music "theory" is completely helpless when describing an EDM track or how to compose one. EDM is one of the most primitive music styles ever (barely even qualifies as music in my opinion) and yet music "theory" is worthless in this case.