No, that effect can affect the strength in both directions, and it's not the reason for the higher ABV in "cask strength" whisky. After distillation the whisky

No, that effect can affect the strength in both directions, and it's not the reason for the higher ABV in "cask strength" whisky. After distillation the whisky is at "still strength" (typically ~70% ABV) and diluted to "cask strength" before maturation. Then after that, it's usually diluted further for bottling.