Well, the main reason I did that was because Cayde referred to us as his protege in the Taken King. I'm trying to keep it as ambiguous as possible, though, because I want to emphasize that the Chosen Guardian could literally be any of our Guardians. They could be an exo, an awoken, a human, a titan, a hunter, or even (it shames me to say this) a warlock.
Ah, I didn't realize Cayde called us his protege in Taken King. I'm doing a similar thing in my story, making you nods, but not giving details, so that the reader can fill in that spot with their own Guardian.