It means the one you got is not interchangeable with the one anybody else got in some non-frivolous way. It's not personalization when fifty other people got exactly the same thing. Buses aren't personalized just because they each go to a different place.

I don't get it. Cars are mass produced, they make millions of them, all same. Between one person's Honda civic and another, what's the non-frivilous difference?

There isn't one. Existing cars aren't personalized by the factory. Some people personalize their own after the fact.

Other examples of personalized things: A caricature of you drawn at a carnival, the local chef who knows just how you like your meal, that thing your nephew made you in shop class, etc.

In tech it usually means using the surveillance the company has conducted on you to make search suggestions and things like that. But people are increasingly finding that creepy and invasive, so it's not clear more of that is going to be a winner in the transportation market. Even historically it has been mostly backfill to rationalize the surveillance. Having some cloud surveillance technology literally following you around and recording your whereabouts isn't exactly the same kind of warm feeling you get from your favorite chef knowing how you like your dinner.

Your car is blue, black, red, or whatever. It may have bigger/wider wheels, a spoiler, a better radio, stickers on its back that express your preferences, those sunglasses in its glove compartment that you never use, but have fond memories of, etc.

Whether those are frivolous, I think is in the eye of the beholder.