I am also curious about this. Has anyone found a different outcome to the one mentioned above?
No, and that's actually the point of Eder's quest--that he'll never know why his brother decided what he decided. You can have a later conversation with Eder where you say something like "your mistake was waiting for someone else to tell you what was right", and he agrees with you, and says "I guess I just miss my brother". His quest is, literally, about *coming to terms with uncertainty*, not about getting answers.
That may well be the case, but in the dialogue about the relic, at a key point I had the option to select a [Cipher] response, and two others, which were red and not selectable, saying [Requirement not met]. This rpg-mechanic at least suggests the possibility of another outcome...