While all salvation is ultimately wrought by Christ’s Incarnation, Death, Resurrection, Ascension and Glorious Coming Again, those of us who adhere to traditional Christianity, whether Orthodox, Latin, Coptic, Armenian or Assyrian, expect saving faith to be something more than assent to that fact and to the Lordship of Christ. Putting on Christ, following His commands, growing into His likeness is part of faith, thus the humble acceptance (in the eyes of his community) of the sins of another, being an imitation of the true saving work of Christ might well be part of real saving faith on the part of the “sin eater”.
Of course the only way to find out whether my suggestion is right will be for those of us blessed to be on the Right Hand at the Last Day to make inquiries among any Welshmen among our fellow “sheep”.