The man was supposed to have been around only 20 years ago. There's no way a ton of people wouldn't remember him unless he never existed in the first place or some strange fruit power wasn't used to wipe him from everybody's consciousness. Seriously, though, he has zero relevance at this point. The whole colosseum wasn't any topic before Luffy heard about Ace's fruit as the prize a couple of eps ago, so who cares about the history of the fighting arena, let alone a single man?
Unless the blind admiral and this Kyros fellow are the same man, and the single wound he ever received blinded him. Though that wouldn't really explain, either, why nobody remembers him, but at least it would grant this story some importance. I guess the pink gladiator woman could be his daughter, granddaughter, or something, as well.