That's because you (unknowingly?) had your Notes app setup to sync with your Gmail account when you added it to your iPhone. For anyone else, to turn it off go

That's because you (unknowingly?) had your Notes app setup to sync with your Gmail account when you added it to your iPhone. For anyone else, to turn it off go to: Settings -> Notes -> Accounts -> <Gmail Account> -> Notes "turn off" to disable Notes syncing.