Not saying that it happened in this case as we shall only really know once the full investigation is complete but I know for a fact that a certain freight forwarder out of NBO whose speciality was shipping fresh produce knew that due to the dry atmosphere on the aircraft in cruise the freight would loose between 5-10% of its weight through dehydration. They would therefore overload the aircraft to a corresponding figure. The first that the crew would know about it would be a close up view of the rapidly approaching red lights at the end of the runway with the aircraft still firmly on the ground.
Obviously climb performance was degraded and fuel burn increased accordingly. However once the aircraft arrived at destination and the crew complained enough to have the cargo check weighed it would of course be down to the contracted figure. And so the process would continue.