Could it be that it was raining or going to rain and he was trying to protect the packages? I have done this--I have used an empty garbage can to protect packages. This kept them "out of sight, out of weather" and the customer appreciated my efforts. I have also used BBQ tarps, left packages in tree houses, in the bed of pickup trucks, etc., all in an effort to protect the package.
I recall one time when I was delivering in base housing. I left the pkg in the storage room where they kept their garbage cans and, you guessed it, the garbage guys took the package along with the garbage, even though the pkg was sitting on top of the garbage cans. UPS paid the claim as will FedEx Ground.