This is an optimization, they're not trying to extract more energy than the wind contains. They're taking 500sqft of wind and channeling it down to 100sqft where their 100sqft wind turbine is. 2mph*500sqft/100sqft = 10mph ignoring all the viscous losses and backpressure, both of which there will certainly be some of. So perhaps instead of 10mph you get 8mph.
What they've done is made a 100sqft wind turbine which would have a high cut-in speed effectively a 500sqft wind turbine with a lower cut-in speed. No magic, just a bit of clever engineering provided that the tower is cheaper than the 500sqft wind turbine.
What they've done is made a 100sqft wind turbine which would have a high cut-in speed effectively a 500sqft wind turbine with a lower cut-in speed. No magic, just a bit of clever engineering provided that the tower is cheaper than the 500sqft wind turbine.