Deutsche Post

Today I had to collect a parcel from Zurich containing my headlamp which I left there. I am not sure why they did not deliver such a small parcel to my mailbox. When I got to their centre in Bahnhofstraße the man behind the counter asked me for my passport which I didn't have but my drivers licence sufficed. Then he wanted to know if I knew what was in the parcel and where it was from! After all this questioning I finally got my headlamp. I am not sure what happens if someone sends you a surprise parcel and you have no idea where it is from or what it contains. Does Deutsche Post keep it?