in water, you've only momentum until you reach cavitation. So, the mixed momentum (the ratio of perpendicular to the direction of flows) will drive the resulting component.
In air, viscosity became the dominating factor depending of the regime of flight and geometry of the vehicle (see Reynolds number).
Here, it's not about having perpendicular flow, but a perfectly linear one in line with the wing chord (the Kutta condition)
Circulation
Lift
By expelling air deferentially along the semi wing span, you affect the circulation, hence, the apparent camber. This create a differential in lift and yaw that once played against the distribution on the other wing, give you a total contribution of Lift, roll and yaw (notice that the test model still bears a pair of rudder what indicated that either the yaw components needs some work or is not efficient in the the range of speed of the model).
Taranis use wing flaps (oscillating deferentially) to create the same effect (actuators).
Notice how their precedent test-model used rotating cylinder in the trailing edge to boost the circulation deferentially from each wing.