Humanity ≠ Personhood, or at least that's the premise here.

For example, any of numerous aliens from many different Sci-Fi universes would almost obviously be counted as a person (though the legality of that consideration would not be automatic), but would not be human.

So the question here was, what makes for 'a person' in any of various ways we use the term, the legal definition being just one of them. Many people would argues that self-awareness, empathy, intelligence, awareness of death, etc. are all qualities that we associate with 'persons', whether human or otherwise.