The engineers involved with the initial snag that the RAT was indicating the incorrect temperature probably thought that the indicating system was unserviceable and carried out their actions in compliance with the MEL where flight not into icing conditions was OK. It is possible that the high temperature the RAT probe indicated was caused by the aircraft being "in flight" for what ever reason heating up the probe, to prevent icing, and the conduction of the heat from the probe heating element caused an overheat indication of the RAT. Was this ever covered by the manufacturers maintenance training course which I presume the engineers attended?
Would this be a case where Boeing have picked up a "poisoned chalice" from the original manufacturer?