 You can be unfree and still have no one interfere with you. If they have the power to interfere with you with impunity at any moment, then you're as much as a slave as if they were interfering with you. So a slave who has a very good master who says like, oh, you can just go about your daily life and I won't mess with it, is still a slave because a master could interfere at any point with absolute impunity.