The story now is ...
They can't possibly know the triggering event at this stage of the investigation, way too early.
I presume they've collected the 'Black Box' Flight Data Recorder and are doing preliminary analysis of the information. However, that only gives the data the avionic system was passing around and what the pilot, co-pilot, and flight engineer were seeing/saying.
Important Point: the FDR does not give the actual state and condition of the mechanics of the airplane but only what the avionics thought their condition was. That thermometer was doing what a thermometer does: record temperature. WHAT was causing the temperature rise will not be known until the US NSTB and Spanish authorities reassemble the bits and pieces of the plane and conduct a visual inspection and analysis. A doo run-run-run, a doo run-run
