The prosecution's case will probably be that she gave him sex and some material items, including payment of a bill as reported.
In return, he is guilty of corruption because he gave her a better grade than what she deserved.
After looking at the pictures of both Mr Tey and Ms Ko, we may be able to guess his defence.
His defence may be that he gave her sex.
In return, she gave him some material items, including payment of the bill.
She fully deserved the grade she got.
Hence, no corruption at all. The relationship may have been inapproprite given that she was his student, but no corruption.