I realised that too, Crypto - after I'd posted! It wouldn't have made sense to say Mal Washington should have been on the list, since the others on it were all winners. Confusing isn't it?
I also think it was a very difficult question. Where would you find a list of who beat unseeded players, even if you managed to hit on the possibility of that being the answer? I'd never have got it. When you posted MO Washington, my reaction was "Who?" and the same when you mention Lewis. We do generally remember only the winners, as the saying goes.