It's hard to tell without knowing more about your interview experience. In general, Americans are a bit less formal about interviews, especially at small firms; they see the interview as an opportunity to gauge your personality and see what you will be like to work with. It's good to show curiosity about your potential employer, and interview them as well, rather than being a passive subject for the interviewer to investigate. It's more important to demonstrate a healthy thought process than to necessarily have the right answers; never be afraid to say that you don't know something, but always be ready to describe how you'd rectify that problem if you had to solve a problem in a hurry.