Smokes, lighters, vapor pens, cabin furnishings are all flammables. Diesel generator could burn. Electrical fire in the passenger area is an issue also. Possible there were cabin heaters, what with Pacific ocean water temperatures chilling the below deck areas.
From the photos of the bunk area under-deck, it looks like there was one way out on the ladder; if that were blocked by fire I guess they were trapped, probably most died of smoke inhalation. Awful, my best for their families.