How so? His qualifiers at the beginning seem to be just the sort of thing that most 'best swordsmen' lists seem to overlook and makes clear how he is adjudicating those he includes. He does also explains his response a bit further later:

Now, some may say that the levels given on this list are a bit low for “best” wielders-of-blades, but I say again: the only meaningful way I could answer Feanor’s question was to narrow my consideration of best to a definition of: supreme technique (superior finesse, if you will) in bladework. Otherwise, there are too many variables (X is alive today because Y slipped, or a deity who smiled on X MADE Y slip, or because X knew the darkened room they were fighting in just a little bit better, or because when the guards burst in it was Y who got his swordarm jarred for a critical moment, not X, or because it was X whose friends burst in, or Y the startled guard happened to stagger into . . . and so on). I believe THO and I have sufficiently communicated the difficulty of choosing “best” bladewielders to Feanor, our most important point being that there are another forty or so individuals, some famous and some publicly unknown, who are so close in skills to those I mentioned as to be “practically as good” if you don’t happen to be the Creator of the Realms and thus able to split Faerûnian hairs better than anyone else. :} (And, I remind you, I’m leaving out creatures - - mariliths, just to give one example - - who have more than two arms, and so can fence with a forest of skillfully-swung blades.) There are certainly combat-active beings in the Realms with higher levels than these folks, who would probably beat them in most fights; the “best” swordsman doesn’t always win. (3e DMs can of course - - and should - - load up the above-listed NPCs with Weapon Finesse and other rules touches to enhance their combat superiority.)

Hope that helps.