Posit — Self-driving as a skill requires natural language understanding as a sub-skill.
Natural language understanding is not just a skill in itself, but might also be a notation that adds to an intelligence's ability to abstract and generalize broadly about the world. This ability to abstract and generalize is key to many kinds of performed intelligence, and self-driving might be a complex enough activity such that it requires a level of generalization power that is a superset of natural-language understanding and reasoning.
A related question is, could a very, very smart but non-linguistic animal drive? I'm not so sure.
There's a subtle but firm distinction between augmenting human productivity and augmenting human intelligence. The first is an economic, capitalistic endeavor first (though productivity contributes indirectly to collective intelligence); the second is a more pure pursuit, I think.