WHBM
In one of the earlier AAIB preliminary or interim reports, it was stated that this aircraft simultaneously flew through abnormally cold air and unlike other aircraft on the route did not descend due to temperature effects *and* it's engines were operated at unusually low fuel flows and unusually gentle step climbs were performed. It seems that these parameters were right at the lower end of many tens of thousands of 777 operational data records.
Further to this a long continuous (or nearly so) descent occurred, so the first time any significant thrust was needed was as the drag rose when the aircraft was configured for landing.
That is likely to explain why the event was, at the time, unique.