Here we must wonder about two things:

1. To whom is this narrative addressed? Almost certainly Egderus, considering that the Superius Frater had promised to leave a present for Egderus should he ever return to Mountain House. However, at this point — i.e., before the rescue attempt and its catastrophic aftermath (which included his own demise) — how would the Superius Frater know that Egderus was returning?
2. Much more troubling is the question of why "this sobriquet" electrified the Superius Frater. In other words, how much did the Superius Frater know? and about what?