IMO that was more likely to have happened at the airport - why would you think the ship's staff did it? And, if it did happen at the pier, then it would more likely be the baggage loaders who do NOT work for the individual ships.
Then, there's always the possibility that you didn't completely lock it tight???
Too bad you didn't put it in your carryon.
Did you report it to the purser's desk? Did they give you any answers?