Ion wind can flow in both directions, current flow direction has nothing to do with wind direction. Consider two pins at opposite charge, their combined air flow is zero. No wind behind either needle. Now point a needle at you hand or out into air, and wind will flow away form the pin. This is because the energy density (ion flow) from the point is condensed into a small area where the ions are colliding with surrounding air and bringing the surrounding air with it, increasing thrust but lowering velocity (ion potential energy). On a large flat conductive surface, the ions can make their way through non-ionized air to it with little obstacle and less thrust since they have lost energy and are traveling more slowly.

It is ion wind providing thrust, it is just a discontinuity of it. The fine wire is able to bleed ions very easily as compared to the aluminum foil which will readily absorb free ions, but barely emit them. Sort of like a diode in a sense, but free ions can only flow in one direction.

p.s. You can prove ion wind by use of smoke. Either current direction.