With people like him you can never really know. It might have been on purpose, but he's dumb enough to have referenced the stereotype accidentally

Since I'm not well versed in these US racial minutiae, I knew about the "White Men Can't Jump" but not about "Black Men Can't Swim" so at first took that post at face value and had a hard time trying to figure what's there to "cancel" until the notes nudged me in the right direction.