The word that best fits the nuances of the situation described in the sentence is "surprised."
The context implies a positive reaction to the quick delivery of the package, and "surprised" captures that sentiment effectively. While "shocked" and "stunned" convey a sense of astonishment, they might imply a stronger, more negative or intense reaction than what would typically be expected in this scenario. "Disturbed" would not be appropriate, as it suggests a negative feeling.