What metaphors are used in I, Robot by Isaac Asimov?

“But the man is quite inhuman, Dr. Lanning.”

Arguably, the most important story in I, Robot is “Evidence” in which one politician accuses his opponent of actually being a…robot in disguise. The statement above is made by Francis Quinn in relation to Stephen Byerley. It is a purely metaphorical statement, of course, because Quinn is suggesting to his colleague that his political nemesis is not human despite all indications that he is. The metaphorical quotient here is undetermined, however: is being quite inhuman a figurative statement asserting that Byerley is more than human or less than human? Where does a robot fall on that spectrum? And are all robots in the same spot?