What is especially promising is that much of his play should be sustainable as long as he keeps playing about as well as the defense in front of him.
He has a 1.68 GA/60 in all situations in the past 9 games, which is insane and likely to go up at some point, but the Leafs are also a stingy 2.04 xGA/60 in those same 9 games... So Campbell would still be doing exceptionally well even if he was only matching the defense in front of him.
And it is not like we are only playing well in front of Campbell either. We are a 2.28 xGA/60 in all situations in front of Andersen (and Andersen is part of the reason it is even that high if you are looking at some of the easy rebounds he gives up) but he has a 2.91 GA/60. Effectively, he is in the territory of goalies who are single-handedly sinking their teams right now. Not quite Hart or Murray bad, but Elliott bad.