What was their interview like? I have had one normal interview and then a very different one so I am trying to gauge what USA's is like.
My interview was a group of 3 but other people had a group of 2. The interview last about 30 minutes where one question is asked and each person gets a chance to answer. Be prepared for standard PT interview questions, but also depending on your interviewer you might get an off the wall question just testing to see how you answer it. I have heard of some USA interviews being very laid back and then others like mine were a little more serious. Since I was in a group of three there were only 5 questions asked, expect more if you are in a group of two.
You start the day with some information about the program, write an essay, tour, and finally the interview. I would expect anywhere from 100-130 people at your interview, depending on your campus (Also Fall class apparently has more total applicants too). In my opinion prepare like you would for a standard PT interview and you will do fine, their intent is not to trick you at all.
Good Luck!