I'm pretty sure any prosecutor would have a strong case on the basis of the text messages and oddly timed calls made by a Teacher to a Student, the history of which remains into the student's phone and on the network's chat history.
Also, and I'm pretty sure on this, Korea has rules against teachers screwing their students, so even if he tried to play it off as consensual, it would still at the least be considered statutory rape.
It's definitely not something I would be smug about unless I were some Epstein-level multi-millionaire, and not a pretty-boy teacher.