Unless specifically stated or for certain subjects, most courses are supposed to be offered in English even if the teacher comes from mainland China originally.
30% fail is the exemption exam, the compromise of the university as many students don't want to test the course. Thus, the university wants to distinguish who can be exempted from PTH course. 30% is not low considering it is an exemption exam.
The fail rate of the course was 5 in last 10 years!