Will Anderson, another Scrabble champion/grandmaster, uploaded a video talking about Nigel's win here. The win is a lot more impressive than memorizing bingoes - Spanish scrabble has different letter distributions and point values, resulting in different metas. He didn't just memorize the Spanish Scrabble dictionary - he learned how to play Spanish Scrabble and dominated the first Spanish tournament he participated in.
In fact, you do need to care about the short words.
1. they can be useful at locking down the board
2. knowing all of the words is necessary to be able to challenge when somebody attempt to play a phony, which, as a native Spanish speaker, you might be even more inclined to try against a non-native speaker.
Do professional scrabble players use fake words as a strategy? I assumed that (minus the weirdo savant playing in a foreign language), everyone at the professional level has an extensive vocabulary for which it would be difficult to bluff.
Scrabble players at world champion level operate at the very edge of what is or isn't a word.
Everyone knows words like "fork", "vogue" and "alligator" but only scrabble players know whether or not "forkier", "defork", "voguier", "voguiest", "alligatored" and "alligate" are real words.
It's not super common but if I was playing against somebody who didn't speak the lingua franca I'd probably throw out a couple phonies to test the waters.
The CSW is the official English word list used internationally (outside of the US/Thailand/Canada because we just HAD to be different) and contains over a quarter of a million words. Unless you're at the UPPER OF UPPER ECHELONS, there's a chance a crafty player could slip a phony in by hooking an "S" on the board or some other subtle stem - especially with the pressure of time controls.