Ok, new information from the wife:
Apparently the last time this happened she asked the landlord if he had seen our bin, and HE told her to put our address on it. Also, apparently some yard work was done on our part of the property. So maybe he thinks he has a right to our bins to do yard work even though that's his responsibility. Because he took it five days before any work was done - it was sitting empty in his backyard until the work started this weekend