I looked pretty closely from a couple of angles; I think it's just a reflection of the lights and the rigging for the lights above. Here's another angle from the slideshow in the article:
If you open the photo in a new window it's pretty clear there's no wiper visible. You can see the gaps between the light elements and the reflection wraps around the side of the truck where the windshield ends. Wipers could just be recessed below the hood. Or they could laser the rain away!
I'm holding out for lasers. Then, when Musk feels upstaged and orders lasers to all the Cybertrucks to replace the Monowiper, they'll be misaligned and blind a bunch of drivers.