LOL - I thought about that, too. There's probably some fire science geek somewhere already running the numbers (maybe for his Master's).

Without getting too geeky about it... From the photos, it looks like the only fuel load in a typical sleeping room are those reindeer skins and sleeping bags (the latter would be fire-retardant, also). If the sleeping platform is also snow and ice (it says so on the web page you linked to), it would melt and extinguish a fire from beneath before sufficient heat got to the ceiling.

My guess is, the only place it might even be feasible to begin melting the ceiling with an internal fire is the bar: plenty of accelerants there. Would it count as fully protected if the "automatic" (that is, inevitable)application of water to the fire degrades the structure?

Of course we know what would happen if there'd been a code review... that's the other reason (besides the weather) why it's in Lapland. ;-)