BOY I hope you either got a side-reply or otherwise figured this out in the last month +. But in case anyone stumbles on this seeking the same info I* wanted to quickly reply that you pick three separate character parts, a Bloodline, an Origin, and a Post, each contributing to your character sheet in roughly equal measure. So you get three edges, because you are choosing that "1 edge" three separate times.
*I am just some dude playing the game, not any particular authority. But I feel confident enough in this understanding to hopefully help you out with your specific confustion, here.