You may not like the answer because part of it is naturalizing players with Hungarian ancestors - like Callum Styles or Willi Orbán, both world class players in my book.
Another thing I noticed is that the shaft of our team - the 3 Leipzig legionnaires - brought some sort of superior "world star" confidence that had the following effect:
-earlier the NT couldn't even live up to its own expectations, we lost to teams worse than us because everyone had to bear the unbearable pressure of the Magical Magyars past - Hidegkuti Puskás etc. Plus a lot of tax money went into development and stadiums so more pressure
-but the players like Sallai and Szoboszlai who developed abroad simply didn't care about that (same goes for Orbán, Styles, Szalai Attila), they just wanted to be the best and so this immense pressure evaporated within a year
Also, Rossi changed things up after the Wales game, he keeps saying stuff like "only winning mentality from now on, winning type players". It's funny because the vast majority of the squad remained.
Something like that. I'm not even saying I understand perfectly what happened cus obviously I don't.
Something obviously changed in the players' head. They went from "we try to lose by as few goals as possible" to "We dare you to attack us with all you got, we gonna kill you off with counterattacks and if you don't attack, WE WILL and you will regret it". That's what I pick up at least from body language (I studied communication).
Fun fact: even the German NT has players who could have chosen Hungary ie. Niklas Süle (Süle Miklós) or Márton Dárdai.