Blazed by a pair riding significantly lower wattage?

I was riding Watopia today and was passed by a pair of British riders. I later looked them up and found that they were doing some sort of 1000km challenge.500km today and 500km tomorrow.
The thing I found strange was that I was riding around 2.3-2.5w/kg (160-175 watts, ~35km/hr at 0% gradient) on the flat Tick Tock course on my Tron bike. This pair zipped past at least 10km/hr faster than me, doing around ~2w/kg, and were gone in seconds. I didn’t notice what the frames they were riding were, but not Trons. Out of curiosity, I checked in on their wattages, and they were low (ranging 110-140 watts which I was watching).
How the heck were they so much faster?