My guess is that this is putting the coils in parallel, not the batteries.

According to that link, the applied voltage determines the speed and the applied current determines the torque. I don't know the exact configuration of the windings in these motors, but having the coils in series should be putting a higher voltage on the motor (higher resistance), and having the coils in parallel should have more current (lower resistance).

Pretty neat way to get a "2 speed" transmission. Of course, it's not going to be as good as the current generation of BLDC motors (variable speed is tricky with bang-bang control...), but for the time it's a pretty clever solution.