What I said above — the “theory” for OOP and related concepts (multiple inheritance, etc) is basically a description of what OOP languages happened to do.
Yes, you can introduce math formalism for it and maybe rationalize it from first principles (people tried that in the 1970s and 1980s), but it does not make it a “theory” with much content beyond the actual language spec. (Which is fine — not everything needs to be a theory).
OOP has been around for 40–50 years in practice, depending on how you count.
These are facts, I am not sure why you consider them insulting.