The description of the paper I reproduced above mentions: “The tethers are connected to the ground station which is parallel to the balloon, and can orient according to the wind direction.”
And the sketch page 4 mentions the “pivoting ground station (6)” . This sketch is reproduced below:
In other words the ground station (6) rotates (by a motor) with the balloon when the wind direction is changing. In addition to be parallel each other, both are the same length, facilitating (at least on the paper) synchronous enough operation. If the sausage is a little twisted during the wind changes, is that so serious?
For the rest, aerodynamic behaviour is effectively unknown for such dimensions.
There is one point: the tangential speed cannot be high, and so the power per m² will remain limited but more than sufficient.