David Hayman proposes that these sentences can be read as revealing to us that the unnamed Narrator is telling some unknown auditor(s) what he saw some time earlier at Barney Kiernan's pub. That is, all of Cyclops would be a retelling that is recounted at some time removed from the hour in which the action unfolded. See annotations here: http://www.infiniteulysses.com/ulysses/321
