By going to the Ameliapedia, then Technical Papers, then The Wreck Of The Norwich City by Janet Powell, she states that the three bodies ( the Steward, a Fireman, and the Carpenter) were "...recovered and afforded a burial on the beach(emphasis mine, hjh). It's not a stretch to believe that the action of the surf, wind, storms, etc might uncover those bones and leave the beach "littered with bones" that might then be noticed by visitors to the island.