it's common with the arts in general. People often attribute to being gifted what are entirely learnable, physical skills. Singing in particular, it's astonishing how quickly you can teach someone to sing well even if they think they sound like a cat in a blender. Unless you have actual damage to your hearing or vocal chords, 99% of the people who think they're tone deaf just haven't learned to listen.

It's a great pedagogical experience just to show people how much of a difference deliberate practice makes.