I suspect, they have a cut off point for the exam and interview is to see if the candidate will fit into the school. Were questions asked about hobbies or sports? My dd found that at her interviews they asked things like this and then would mention they had it at the school, or would say things like you would like that here or we have that etc. She interviewed at FHSS last year and enjoyed it. But I think it also depends who you get and if they might be short on time. Just because an interview is short, does not mean all is lost. She had 15 mins with G&L and I was wondering the same, how can the assess them etc. Somehow, they manage.
My ds is now year 5 so I am curious how the interviews will go with the boy schools, if it will be similar or if they will ask more tricky questions.