My guess for the "nav mesh" is that it will be a GPS-like thing where you can set a waypoint & it will tell you how to drive to there... Just like in GTA
To me it looks like a mechanic to make the AI stay on they're own side of the road. If so then I'm looking forward to that!
I love games like this where you can see all the code and understand how the game have been made. Everytime i see something in the code i'm like "It's too well done" x)