Having read all the posts again, the only one really is relevant in all the speculation... valipilot explains it very well....
Ignore the A/T.. 2 servos that drive the throttles. The throttles were pushed forward manually which overrides whatever a/t position was commanded. The TLA's (resolvers mechanically connected to the throttles and powered by the EEC's) send the EEC's commanded position.. forget autoflight/throttle the throttle position commands the relevant fuel flow/ EPR (it's not like Airbus).
No one knows (other than the AIB and the crew) whether the engines were running on touchdown, the only conceivable way if not is both master levers off (highly unlikely) or coffee spillage in the switches as a posibility (but again not very likely). If NAI had not been selected, again there would be handling problems and signs of surging/ EGT fluctuations when icing became apparent
If they were stuck in idle then it's EEC's controlling this.. rev unstowed would cause it but a dual failure again very unlikely so again it goes back to software.. an aircraft system input to the EEC's or EEC algorythem demanding min idle. Aircraft system interfaces generally demand more fuel, ie ECS demands, anti ice, flap position so unless there's been an electrical spike down a databus or dicrete line in then this can be ruled out.
Fuel contamination / icing could cause engine problems but you would expect somekind of surging or engine control problems earlier and most probably fuel filer bypass EICAS warning, not just not responding at idle. The heat management system (FCOC/ oil heat exchanger) preheats the fuel to prevent fuel waxing on the engine to prevent FMU torque motor problems.
EMI interference is another remote possibilty but then again i've used company mobiles during turnrounds and engine runs and they never even make the lcd's blink let alone interact with the current couplers!
Either way the flight crew had no time to troubleshoot or even work out whats going on so forget gliding angles, flap position and gear up/down and just commend them on bringing the airframe to a halt with no loss of life.