I noticed it when I moved to the Bay Area after growing up in western New York. The types of foods people ate or didn’t eat, the restaurants people would or would not go to.
The shows people would or would not watch, even the way people talked. I think I hadn’t really seen the difference in class behavior before in America. Now it’s easy to see it.
A lot of it is tightly correlated to wealth and a lot of it reminds me of things the author describes (fear of not being able to find a job, fear of just “taking a year off” because it sounds financially crazy), but it’s not only about wealth really.
You can be poor and still act more “upper class” and you can be rich and still act “working class”. It’s a lot of little things people do in preferences and how they talk/behave.