Super Humans are those who possess normal brain function, but like a super athlete, etc., there is a likelihood that chemistry lines up in such a way that the larynx & brain in the case of Jackie, or the arm & the brain of a tennis pro are in perfect union to create the sound or the serve that dominates all other humans in their age group.
Is it ART? In Jackie's case, she talks about feeling as though she is 'possessed or something' when she sings, as though her physical self only provides the conduit to a supernatural experience. She simply provides the voice to "show that miracles can happen", in her own words. I tend to agree.