The bag could have ripped when they lifted it and they put it back down. They could have told them inside what happened and this is what they were told to do rather than have one bag short till the next delivery. Obviously if the bag was ripped for a long time, there would be spillage in the truck and the bag would not be full and therefore they could not charge the full price for the bag, therefore there would be a discussion about it. They couldn’t just sneak it in.
We really need to be dan l’kaf zchus in all areas of our life and stop looking for the wrong and the bad in every situation. WE can think of so many scenarios when we come upon a situation but we really are just letting our imagination take control. WE really don’t know what truly happened.