They may be taking advantage of some geography. In a town I used to live in, Spruce Grove, it could be a light breeze from the west. However, Spruce Grove sat in a slight valley which funnelled the wind into a more narrow space and the force of the wind increased.
Maybe something like that
See above, and this video below.
Ice Yachting - The fun and fear of 100kph
Feb 22, 2019
Capable of more than four times the wind speed a DN ice yacht can reach 100kph and in a fleet of 50 boats the closing speeds are both alarming and intoxicating.
https://www.youtube.com/watch?v=PE8mCZOmrEo&ab_channel=TheWorldSailingShow