Correct! Good for you Monica. Many know this work or would instantly recognize it, but perhaps didn't realize this theoretical feature. The 1st movement is in C Major. The Exposition does the coventional modulation to the dominant key (up a 5th). However, at the end of the short development section, instead of preparing for a return of the tonic key for the recap, Mozart instead prepares for the opening music to return in the subdominant ket of F major. Why would he do this? I can only think of one reason: the same path/pattern used in the Exposition (i.e. the modulation up a 5th) here will now return the music to the tonic for the ending.