FWIW - I do think that can just be an anomaly. The fires Carnival has had 9until Splendor) were small and not serious at all. One ws on the rope deck and probably the result of a person smoking, and the other was a welding job where a spark lit something.
Other ships have had fires; Princess, Norwegian Epic had several setbacks in the shipyard including two fires, one of them serious enough to set the ship back by a week.
Fire at sea is a very bad thing - but when you are dealing with such a complicated machine - an electrical plant, engines, smoking passengers, etc, it is bound to happen once in awhile. The more important point is how it is handled after the fact.