Good 'un, rum.

My point is that onboard catering sounds like some kind of specialized activity.

Many, many cruise passengers are groups traveling together, whether they are extended families or organizations or company-rewarded employees. Might 'catering' refer to them?

It's just hard for me to believe that food is NOT included in the purchase price of a cruise.

On US trains and maybe also in Canada, when you have a berth or stateroom food in the dining car is included in your ticket, but sometimes does not include the snack car.

(Train trip before last, our train ran uut of food. Not to mention water. And toilet facilities. At a certain point they freed everyone to go to the snack car and eat whatever they had there free of charge.)