This article was in need of a windtunnel video showing the effect: https://www.youtube.com/watch?v=mVJjn1pt08g . The right type of plasma can reattach separated flow. (https://en.wikipedia.org/wiki/Flow_separation).
There's been work on kinematic viscosity changes due to plasma effects in plasma torches, but I can't provide links right now.
It will be interesting to see how this holds up in real flight conditions: icing, bug splat debris on electrodes, low pressure at high altitudes, and how much electrical power is needed to sustain the benefits. Cool work.
One guess could be (as the WP article above seems to imply) that kinetic energy that would normally go into turbulence instead goes into ionizing the neutral gas (i.e. surrounding airflow). That would transfer kinetic (turbulence) energy into electrostatic energy, and thereby of course reduce turbulence.
But this is just a hunch.