There is more information to this than just a coach who led Girona to the top of La Liga with his "cool hands". Girona is well financed. It is not a club that came out of nowhere and played its way to the top with mediocre players. They have invested big time in infrastructure and they have a well formed team within the club that understands how to build football teams. The City Football Group is backing it and they have the money to make sure that the coach stays if they want to keep him. By now the City Football Group owns 12 clubs worldwide. The chairman of Girona is so called Pere Guardiola, got it? 
The brother of Pep Guardiola. There are no amateurs at work.
That's the whole point of The City Football Group. They have "invested" heavily into these clubs, as in they are literally making their small transfers for them. Savio is going to City as a basically thank you from Girona, surely they are basically getting the most out of this deal, but they are benefiting. The brother of Pep Guardiola. There are no amateurs at work. Teams like Girona, Palermo, Troyes, and many more who are playing in their respective leagues, with backing from this group, and getting a huge amount of scouting network. When one player shines, the group basically puts that player in one of these clubs. It's literally a different way of having an affiliate club, you could just loan any player, but it is basically done in a new form. This helps build City to always have their pick of many players.
It is indeed a strategically interesting construct what they are building. Not only do they have all these clubs around the world, but also are they building these ties with scouting agencies and so on and so forth. They are building academies for young players as well. All of that can feed the biggest clubs they have with the best talents while players that are not immediately making it, can be sent to the other clubs for development.