I’ve had it on faster solo* mtb rides. makes you feel good.
A fairly flat woodland singletrack ride, I’m happy and exhausted with 9mph average speed. Proper red zone efforts, high heart rate throughout etc.
even on mtb tyres that is a gentle effort average speed on the road. If you generally only ever strava “proper mtbing” then I can see how it would look different to the algorithm.
*I think the not stopping element really helps here, as I’ve not had it when I’ve been the weakest in a fast small group ride.
eta:
I’m guessing it does it based on sustained 25kph speeds on the flat with very little above.
I’ve had it on a solo winch and plummet sufferfest lapping of Peaslake/Holmbury. very little flat and certainly no sustained 25kph.
So it cant be solely this.