Apparently they figured out how to do it, but my question is, how exactly are they doing it?
A boat has a displacement that is less than water. Which is how it floats. A small weighted bulb in the keel keeps everything pointing upright. You can mitigate the forces on a sail through 2 ways: heeling is when the entire boat leans to one side, heading up is pointing the wing sail into the wind.
Wingsails are pretty well understood and used extensively in racing. Volvo Ocean Racing (VOR) and America's Cup are 2 examples.
One advantage of this kind of wing sail is it's "self trimming". With the tail/tab in neutral position, it'll always weathervane to follow the wind. With the tail tab deflected somewhat, it'll weathervane with some amount of angle of attack. So even in very heavy winds, all it needs to do is back off on the angle of attack and it should be in a relatively stable state.
But to be honest, I have very little knowledge on this topic, so maybe a keel is all it needs!
On a traditional boat the sails can dig down in the water and needs to be released rather quickly, and you don't want the hatch to be open, but neither of this seems to be a problem here.
That said, I don't know much about sailing other than it being on my bucket list of things to learn so I've been reading up on it, and I've been actively searching for a good simulator that works on gnu/linux... (anyone know of one?)
I suppose though a drone has more flexibility in design parameters by not having people and people-related supplies on board.