I thin it's mostly due to the fact that he spent 4 more hours than zverev coming into the match. It's his first slam ever btw, never played bo5 in his life before and just played 3 5 set matches this tournament. Zverev did relax a bit after winning the first admittedly.
I think the chances of him improving as much as sinner are lower than 30%. I would never predict someone to become this good without major evidence. Sinner will retire as a top 10 player ever at least if not top 5, I believe. Jodar is not very fast he'd need a major ugrade there, Sinner is also a top 2 returner of serve on tour, a top 5 server and maybe the most consistent machine from the basline in the history.
There's a world where Jodar can become a Sinner 2.0 but i think the chances are very very slim for now imo.