The phys.org article mentions it: "[...] the team carried out static and dynamic tests in a wind tunnel with a variety of wind speeds and ground surfaces under a low atmospheric pressure of 17 millibars.

Results showed that wind speeds of 9–10 meters per second were sufficient to set the rover in motion over a range of Mars-like terrains, including smooth and rough surfaces, sand, pebbles and boulder field."

Ah, thanks, I missed that. It's weird how that information is in the phys.org article but not in the linked abstract. I guess that's because it's just an abstract -- they must have given more details during the presentation.