Trust me, I know how the cabins are put together, and have dismantled them to make repairs behind the walls.  The cabin wall panels are what they are almost assuredly talking about, as these are the only fire rated panels used on ships.  Whether the shipyard assembled the cabin (which as you say they don't), or whether a sub-contractor builds the cabins for delivery to the shipyard, makes no difference if the materials do not meet the requirements.