After seeing that appearance yesterday, it’s a lot more likely that he’s practicing it for actual usage during the regular season, which would put him on a rather rare list of pitchers.
The recent history (since 2007) of non-knuckleballers throwing the knuckleball is very short. Eddie Bonine used the pitch the most when he worked it into his repertoire with the Tigers (232 Times), Ryan Franklin sparingly used one in relief with the Cardinals (26 Times), Manny Parra of the Brewers “fooled around” with a knuckler seven times (an even rarer lefty knuckler), and Livan Hernandez threw it once with the Mets (because of course he did).
What does it mean? I don’t know. There’s so little history of it, and it’s especially weird for a guy who put up a closer-worthy season and still has closer-worthy stuff to debut the pitch.
In the tiny sample size we’ve been able to see thus far, Wilson appears to have a decent grasp for command of the pitch, and the knuckler has had consistent late movement down and in to a righty. So like with Vicente Padilla‘s “soap bubble”, it might just work if not overused.