Can you explain how it's wrong? Obviously, normally you want things to scale more slowly rather than faster, but other than applying to a different thing than usual, it seems accurate to me -- human drivers improve at a constant rate regardless of how many there are, and self-driving cars improve linearly with their number.

A function being in O(f(x)) means the function grows no more than a (multiplicative) constant factor faster than f(x). So O(1) is a subset of O(n). O is analogous to <=.

The semantics that GGP comment meant to convey are better represented by saying that autonomous cars' driving experience grows with Ω(n) (analogous to >=) or Ɵ(n) (analogous to =).