My experience has been the same as the author's. My college classmates (at Swarthmore) and I were repeatedly surprised when we learned that our friends were trust fund kids. I remember junior year we found out that one kid was super wealthy because he bought a last-minute cross-country plane ticket, first class. Even his roommates, who had lived with him for years, had no clue he was wealthy.
Another time, I learned that a girl was wealthy because she bought an iPod ($400 in 2004!) on a whim. I'd previously thought she was upper-middle class because she drove a Honda CR-V and didn't have any other trappings of wealth.