I don't know what caused the turnaround but it is fascinating.
I'll tell you what though, if his turnaround is as legit as we all hope, he's going to be the poster boy for every franchise in the next ten years who drafts a QB who struggles early on. "Just give him some time, remember what happened with Bryce."
I think his example will create a patience in fans and front offices that hasn't been there recently.
There had already been a slight shift in terms of how media and fans think of young QB's coming into the league. How the Bust label is written on them prematurely, and how organizational competence has a lot more to do with the Busts and successes than we realize. We see what Mayfield is doing and then look at the current Browns. We see what Darnold is doing and look at the current Jets. Neither one are surefire Franchise guys necessarily, but they are proof that organizational competence + time often turn what one deems to be a bust into QB's you can win with.