They referred him because he revealed that he had the girl as a SM friend. So, someone there was alert and investigated further. It would have been better if his over familiarity had been nipped in the bud before, of course.
The horrifying point of the panel is that eh would be a loss to the profession because f his results and teaching. It is abhorrent to me that , had he been a bit crap, they would have sized the opportunity to 'hang him out to dry' but because he got decent results he is protected. That said, I would be surprised if he finds work as a teacher in the UK now.