alt Hacker NewsI think OP makes a good case that the cause of the fire was probably the shortsighted poisoner, child rapist, human/dog murderer, embezzler, thief, and bomber who apparently had grudges against the captain who mysteriously died shortly before the fire mysteriously started at the worst time & place possible.
At least from Wikipedia's description - of the ship as a disastrously ill-designed firetrap, with lackluster officers and crew - there were an extremely large number of "worst times & places" for a fire to start.
(BTW, you forgot to implicate the story's villain in the ship's poor design, weak cadre of officers, and the departed captain's slipshod safety training:)