Fine mist can trigger fire sensors - including such mundane things as spray-on deodorant in an airline lavatory, especially if aimed upwards at the sensor.
I'm not sure whether decompression could cause sudden mist in the cabin; you have to decrease pressure sharply in an already-saturated atmosphere to get large-scale cloud condensation, and aircraft cabins at 37000ft are very dry. So I think it is unlikely. Does anyone have any contrary data?