You can train yourself to have perfect pitch too, it's a lot like relative pitch but you use music you know well as the starting tone. "This note sounds like the opening chord in x song, so it must be A major".
I can attest to this being true. That is how it started for me. But it isn't like relative pitch (all practicing musicians have well developed relative pitch) -- it is more like seeing colors or feeling textures. I have noticed that most of my colleagues with perfect pitch are pianists. I think it helps to have that same pitch always be reluably the same. Few string or horn players have perfect pitch on all instruments, but many do have it for their own instrument only.