I've seen this happen before with human remains. The aft cargo compartment in an A320 comes with a couple different configurations. When I worked for America West, most of our A320s were configured with two aft cargo doors. One large door like the one in this video, which all A320s have, and one smaller cargo compartment door behind that for smaller cargo bin in the part of the tail that slopes up. This one is much smaller and we referred to it as "the taper". We carry anything in that compartment typically, I'd say less than 5% of the time, and when we did, we usually took down the cargo netting and loaded it from the main aft bin rather than through the smaller compartment door. Some people would forget to peek over the cargo net to make sure it was empty. It was common to find override bags in the taper that should have been ofloaded. When this happened, we counted the bags and sent them back on the same aircraft if it was returning to its origin. We'd also leave local bags in the bin sometimes that should've been offloaded. I remember one occasion where a Human Remains (casket) overrode from Phoenix, and we sent it back on the same aircraft, alerting cargo. BTW, no U.S. carriers have container loading systems for their Airbus narrow-bodies, as depicted in this video. This system has been adopted by many European carriers and some Asian airlines. Air Canada is the only North American airline I know that does containerized loading on their A320s. I believe the A319s are bulk load. A320s with container loading, the taper is used as a bulk bin (like a widebody, where you could load strollers and special handling bags.