兩碼事

两码事
liǎngshì
two things that are fundamentally different from each other; two very different things

CEDICT

two entirely different matters

Wiktionary

性質不同不可牽扯在一起事情:「問題我說兩碼事根本風馬牛不相及。」兩回事」。

重編國語辭典

Entry Composition