Statistically on a sinking ship a sailor who couldn’t swim had better chance of surviving than a sailor who was a good swimmer. In a cold Atlantic water the former had been expending less energy then the later, so he would last longer until being rescued.
I don't know about the statistics, but I'm descended from a small Scottish fishing village and remember being told that sailors didn't lean to swim. The logic was if you went overboard you were dead, the non swimmer would suffer less as they'd drown sooner.
I'm not sure how much truth is in that, and I doubt it applies these days as it was probably from the days of sail when a ship couldn't just stop & turn around.