I have seen two other postings for an iPhone box arriving empty from the delivery company. Thieves target jewelry and money-items because they are small and easy to carry but also valuable. iPhones are easy to lift during shipping for the same reason. Apparently UPS is getting tired of reimbursing at least some claims (maybe they used a temporary third-party for one step of the process).
Any iPhone delivered to your house is a target of thieves ... one poster swore he was home when UPS says it was delivered "to the person at home" but the poster never received it.
Apple Stores can be delivery points for your device because Apple Stores have employees to hold your product safely.