两码事

兩碼事
liǎngshì
two things that are fundamentally different from each other; two very different things

CEDICT

two entirely different matters

Wiktionary

性质不同不可牵扯在一起事情:「问题我说两码事根本风马牛不相及。」两回事」。

重編國語辭典

Entry Composition