Is Shrodinger's cat epistemology or physics or both?

In fairness to the truth of the notions referenced in your question, both.  People who know the fields/topics you reference say "Both":  https://www.youtube.com/watch?v=DHc-lrt9N7g 

While Schrodinger's cat may typically be cat-egorized as physics only, in fact it was intended by Schrodinger to illustrate the epistemological divide between quantum positivism and classic macroscopic determinism; in other words, decoherence per observer entanglement seemingly necessitates the irreal positing of positivistic superpositionality of quantum eigenstates as a type of reductive "assume a spherical cow" convenience.    

Quantum Physics

PHYSICS. Epistemology is a theory about the validity and scope of knowledge itself and how  justified belief is differentiated from opinion. The "Schrödinger's cat" thought experiment was created by physicist Erwin Schrödinger to illustrate an apparent paradox of quantum superposition. It does not question the validity of knowledge, it questions the exact point when the status of the cat can be determined. It was not intended to be an epistemologic theory.  

Physics