It's really tough to discern whether the tires are studded or not, but I'll take your word for it. Cool pics nonetheless.
Studs excel in hard packed snow and ice conditions. That course looks to be fairly light snow and soft dirt. If this was a two day event on the same course and the surface layer of the snow had melted a bit during the heat of the day, then refrozen overnight leaving solid sheets of ice and packed snow on the course, I'd imagine a racer with studs would dominate on the second day of racing.