It comes up in virtually every article about automated cars, with zero explanation. If it really is just that journalists are too afraid to ask / don't know better, that's pretty damning for the entire tech journalist industry!
I've noticed that.
If you were just doing car to car communication for automatic driving and didn't need to send ads, track, or remotely update the car, the way to do it would be through the vehicle radars. That's how aircraft send altitude, ID, and anti-collision data back to the ground and to each other. Since you know the range and direction of the signal source, totally bogus signals are readily detected. Doesn't even need a permanent ID; choose a big random number at each start.
But no. The anal probe approach is essential to so many business models.
In a vehicle application wouldn't that suffer heavily from line-of-sight problems?
Second, supposing you did need connectivity to have a self driving car, the challenge is having a good signal everywhere, not having 5g. You can't even get 4g everywhere.
Third I would never purchase a self driving car that requires any connectivity in order to work well.
Communication is quite a key to solve the task, but I believe the entire framing of the problem is wrong: you don't need a self-driving car, you need an automatic road.