I think it was just a couple of them that got startled and looked suspicious or maybe he was there long enough to spot them whispering. After he called them out, I don't remember if he just checked their sheets and notes and let them return or if he called them to continue the test in another room under stricter supervision. I doubt that the students got wronged or treated unjustly in any way. The assistant might have pointed them out or something but I don't really remember all the details, just the brief anecdote.