not that idiom
并非，并不是说
used to say you are not suggesting something
She wouldn't tell me how much it cost - not that I was really interested. 她不愿告诉我这花了多少钱——倒不是说我真的想知道。
（用于表示认为某事不重要）并非
used to say you do not think something is important
Not that I mind, but why didn't you call yesterday? 虽然我不介意，但你昨天为什么不打电话？