I think that argument is nonsense. The whole point of describing a chair as "amoral" would be to point out that it cannot be moral. And when you point out that a person is "amoral", you generally mean that they are not capable of being moral.
See if your friend has a problem with this: "When a man shoots someone, we blame the man, not the gun. The gun is amoral. The man is capable of being immoral."
I can't imagine what could be described as "amoral" under your friend's rule, since "amoral" means incapable of moral distinctions. Perhaps people with some kind of brain injury -- but wouldn't they be incapable of being moral too?