Elliot, at the survivor's new camp and unconscious, is awoken by Hurley. Hurley informs him that he has been gone for two weeks, a period of time Elliot apparently has no recollection of. Hurley also informs him that the other survivors are beginning to get very suspicious of him and his convenient memory loss, especially after Ethan kidnapped Claire.
Elliot was apparently kidnapped by the Others on Day 2 and held for two weeks that he cannot remember. During that time, the tide on the beach at the crash site began to sharply rise, eroding away the beach and submerging the fuselage. In response to this, the survivors moved their camp further up the beach, with this new camp being the camp Elliot wakes up at. Since he was gone during this camp's founding, him waking up at it is his first experience with it, thus making the title - "BACK On The Beach" - somewhat incorrect.