There are some other reasons that account for a native English speaker's success in oral English class, e.g., the teacher's personality-- being humorous, friendly, etc.
Unfortunately, there have been cases in which native English speakers have turned out to be poor teachers in oral English classes because they have no teaching experience or teaching training. In these cases, the students may simply have some listening practice or gain little at all if the teacher speaks non-standard English or always speaks too fast for the students to comprehend.
In comparison with a native English speaker, a Chinese teacher of English in oral English classes may have some disadvantages in language proficiency and in familiarity with western culture. But having got a Bachelor's or even a Master's Degree of Arts after four or seven years' of postgraduate or graduate study of the English language, a Chinese teacher, though a non-native English speaker, should understand how to teach English.
It's also possible for any Chinese to learn about foreign culture through various ways. Whether the teacher can succeed in oral English classes seems to be a question of whether he/she has proper psychological elements and knows the right way to manage the class.
In teaching, a Chinese teacher of English may encounter some of these problems.
He/She may find there are almost nothing new to the students in the textbooks, so he/she may wonder what to teach in class.
He/She consults some information for something about foreign culture and brings it to the classroom, which really can arouse students' interests of listening but changes the oral English class into listening practice. And the teacher himself/herself makes great progress in speaking English but is usually over-exhausted because of the long time of which the teacher speaks in class.
He/She asks the students to read or recite dialogues, but they make little improvement in expressing themselves appropriately in interaction activities.
He/She tries some classroom activities, e.g. pair work or group discussion, only to find that some students remain silent or speak in Chinese or are constantly looking for some new words in the Chinese-English dictionary.
These problems emerge because Chinese teachers of English have been accustomed to teaching English by telling students the uses of new words, expressions and grammar points, and by asking students to recite or memorize something, so, oral English, which can not be "taught" at all, becomes a difficult course for them to handle.