One day I even played a number of "speed" games (3 minute games, those were fun!) against Trey Wright, the winner of the National Scrabble Championship in 2004. IIRC, I beat him in one game, by a single point, while he thrashed me in the other 9 or so.
In order to compete against these guys, you have to basically learn words for no other reason than to use them in Scrabble games. Word definitions are useless. It's a bit of an addiction, and quite pointless, but it's fun when you actually end up playing a bizarre 8-letter word (e.g. OENOMELS) and win the game because of it.
It's absolutely true that language has little to do with being good at Scrabble. I used to play against Thai players who had very little knowledge of English but who knew way more English words than I did or ever will.
Of course, when online, you pretty much have to expect that people will cheat. Most of the time, the cheaters are obvious, because good Scrabble players recognize cheating when compared to real human game play.
As for Nigel, the guy's not human. I don't remember if he was ever on ISC (many of the top players were at some point), but everyone in the Scrabble world knows him and knows his uncanny word knowledge and Scrabble abilities.
And if anyone's interested in reading about the Scrabble tournament scene and the associated lifestyles, check out Stefan Fatsis' book "Word Freak"[3], probably the best Scrabble book ever written (although it does contain quite a few f-words, thanks to the colorful personalities that it describes, which I wasn't crazy about).
[3] http://www.amazon.com/Word-Freak-Heartbreak-Obsession-Compet...
https://www.amazon.com/dp/0142002267