No, it was intended to impart the idea that the primary difference between imagination and hallucination is whether you can tell the difference between the two.

Yes, very yes! Talking to oneself is considered to be a sign of madness in folk psychology, but in actuality everyone talks to themselves constantly and merely represses the exterior component of this discussion to an incomplete degree. (The nerves of the larynx still react, making it theoretically possible to 'read someone's mind' by examining the electrical activity of the throat.)

People who hear voices aren't fundamentally different from normal people, except that they attribute their own internal thoughts to other entities instead of perceiving them to be self-generated. There's actually very little reason to think that the auditory system of such people acts differently.