I don't think that part of the tire is open to the outside -- you're seeing a cross-section in the pictures and video.
For airless tires I've used a 4x4 (quad), the tires are open on the side just like these images.
For a passenger vehicle application, these tweels will have sidewalls. You don't hit highway speeds on your quad and that makes all the difference.
In fact you can see that the photo of the EV on their site has sidewalls.
These tires have sidewalls, the spokes are not exposed. Without sidewalls these tires would be very loud on the highway, and would have a much higher rolling resistance.
I thought that at first too but then wondered if the views are simply a cross section, where the final tire will have that part covered as a regular tire would with rubber.
Completely guessing, but I wonder if they designed the "spoke" baffles to pinch in under the load and thus expel any stones that might fit between them, like a pebble squeezed between your two fingers and shooting out.
A pebble shooting out of the upper side of a tire of a car at 250 km/h is probably as bad as a bullet. Probably worse.
So about the same as a pebble that gets stuck in treads or kicked up by same? Definitely better than a bullet though just by nature of lower speed, what it's made of and because of its poor aerodynamics.
These spokes seem to be able to fit larger pebbles that may be launched from the side of the wheel and escape the wheel well.