Incident seems very interesting: the described jump in (apparent) temperature could well point to ICE CRYSTAL ICING.
The remark of "ice on unheated engine parts" and "unpredictable and poorly understood meteorological situations"also seem to point in this direction.
Would be a first case of BIG engines being so influenced, so far smaller (business jet types) have been influenced.
It does seem to indicate GE's are indeed a bit touchier than P&W with regards to icing matters.
This is definitely being investigated as ice crystal icing, and I can reiterate that it's a "poorly understood meteorological situation".
Other 'big' engines have been affected by ice crystal icing - the CF6-80C2 has had a significant number of events and the PW2000 has had some recent events. However the recent 747-8 event is the first known event where significant engine damage resulted.