Just trying to guess without a translation. I Believe that the teacher called the student after discovering some videos of female students getting fucked spreading around the school and discovering he was doing it, was asked to stop and revealed he knows that the teacher is a bitch herself and forced to her to fuck with him to keep silent and skipping any punishment. Even possible the video is the teacher herself and the guy discovered she was a slut when she was a student and blackmailed her with that knowledge, maybe hinting that giving away her ass was how she got the job?