Something must have changed about his course, surely, for the Student Loans company to make this assumption. Quite apart from the NUS, he ought to go the University Administration office, since I believe the Student Loans company get their info about course attendees from there. The original assertion about the change in circumstances must have come from there, I reckon. Unis aren't in the game of trying to make life harder than it is for students.
BTW, the stakes on this are high if he lives in a shared student let. The house becomes assessed for the whole Council Tax sum, less the 25% for one assessed person (non-student) living in the house. Trying the get the other students to cought up their proportion is a blood from stone job - since they will probably feel that it is he that occurred the CT liability.