iirc from what little history they know about the Supermen and from past Superboy newslinks stories where he talked about himself, Superboy was originally Superman's clone, created to replace him during a time he temporarily seemed to have died. (Cloning was way less regulated in the past and he was created by some kind of clandestine organization.)
So he may be calling himself Superman because he's from a time before the original Superman returned.
Re: THE SUPERMAN CONUNDRUM
So he may be calling himself Superman because he's from a time before the original Superman returned.