Ok, looking at this again, its definitely a windshield. You can see the Y shaped black section where the autopilot camera will be mounted in the top center. I think the diagonal cut in the lower left is for a wiper.
Still not convinced it's a Cybertruck window... but it might be, doesn't match the other cars, the fact that it is flat and tapers towards the top checks out. The curved top is interesting. That's a lot of surface area for a Model 3 or Model Y.
I rewatched the video several times after this posting. It does look more like a CT windshield than any other Tesla vehicle and it does seem quite flat. The sides do look like the wrap around a bit but the patent they spoke of recently allows for that. Intriguing to say the least and I wish they would make other videos like this one.