Read about how high performance wind vehicles sail up wind, iceboats can sail within 10 degrees of the true wind. It's the same principle.
Here is the official site for the records the craft has set, both down the wind (2.8x wind speed) and into the wind (2x wind speed).
http://www.nalsa.org/DownWind.html
I was skeptical this morning, now I am coming to understand it better.