Several reports I've seen say this was a downhill run, working within an agreed limit of power sent to the power grid. I saw part of a presentation by one of the railway's managers in which he was making a big thing of how many homes it was powering - odd, since this was only done for the RhB's benefit. An example
from trains.comThe record-breaking, 100-car train was 1,910 meters (2,089 yards). It left Preda at 2:20 p.m. and shortly after 3:30 pm. crossed the Landwasser Viaduct. The 15.6 mile (24.93 kilometer) journey from Preda to Alvaneu, was downhill starting over a mile above sea level (Preda is at 1,788 meters, or 5,866 feet) and descending nearly half a mile to 1,000 meters, or 3,281 feet. During the descent, the train — which weighed 3,300 tons (or 2,900 metric tons) — was using electrical regenerative braking and generated 4000 kilowatt-hours of power. It travelled mostly at around 20 mph.