This says more about you than her. You are reading way more into it than is necessary. Having been a regular bus taker in a major metro area for many years, I would absolutely have to agree with her "You never know what kinds of people will be on it." That isn't classist, it's just observational.

I can't tell you the many many different "kinds" of people I've encountered on busses and other public transportation. And yep if you had run into these same people, you would be seriously thinking about driving too.