Variance is expected but over 20 games? No, unlikely. I would bet against that happening. And if you look at the data (some great charts showing this that I recall), Fred's variance in his play was at the top of the league. So for him, I would expect higher variance; Jack did not show that yet throughout his early career. Fred ended up with a similar save percentage by year-end but he was nowhere near consistent at all. League-wide there is a certain amount of dips and surges in a goalies play, but it's not quite at the level we've been used to as Leafs fans.
Plus a 20 game stretch of .940 play has zero predictability on what he does over the next 20 games. It doesn't suddenly mean his next 20 games will be in the .870 range. I need to see data if that's the claim here.