The 2th finger, feels far more natural as you reach for the D5 chord with C# as a transition point, compared to the only other choice one has, since the other three fingers are unavailable, where the hand has to expand really fast from a closed position when one tries to reach for the D5 chord after striking the C# with 4nd finger. That kind of motion is ubiquitous in this concerto, though, i.e. the repated tones at the exact same passage.