David goes to China

Last exams for the module were this week. My conversation partner and I conversed haltingly in Mandarin for about 7 minutes; this was recorded for marking.
Then about 20 minutes of the teacher saying stuff in mandarain and us guessing what she said.
Not too bad and all done now.
I'm reasonably confident that I've passed these fairly artificial tests, but I can't figure out why my partner can understand me but the flunet Chinese speakers in Beijing pretended not to...