Lists can be public or private. If they're public, the account being added gets notified. If they're private, there's no notification, and nobody else can see t

Lists can be public or private. If they're public, the account being added gets notified. If they're private, there's no notification, and nobody else can see the list or its contents anyway. "if you put me in a list, I will block you" is almost certainly about public lists, either because the notifs are noisy or because the list may not be a flattering one.