Sounds like the advisor pushed the cost of 1 rotor off on to Fiat in the form of warranty. Having been a service advisor I can tell you he could lie about one rotor, but if he tried to do both it would have been kicked and he would eat the cost. Brake noise is what we used to call "lot rot" it's when brakes sit on a lot for awhile and rust up. Most of the time a couple hundred miles of use calms them down, sometimes you have to turn them. Rarely are they replaced.