Actually 1:45.86 to 1:42.82. Part of the big improvement is that he finally got into some very fast races.
He got in a 1:43 race in Monaco and ran fast. Then he got into the fastest race in history and ran fast. I wouldn't be surprised if he never runs faster again. That's no knock on him. It's just unlikely he'll have a WR pace setter again.
As a top-5 finisher he will be tested. Innocent until proven otherwise.