Other mistake: They act as if Carson was part of the dojo with the whole crew, but Kim was a Black Dragon when the show started.
Other mistake: They say that when Jack is back, they will be in college, but they were in Year 8 and all 14, so they would be, at most, in Year 12.
Answer: If you noticed, Kim was not sitting with the Black Dragons, so it's safe to assume that she didn't approve of their bullying tactics. She also flashed Jack a smile during the fight, so it's pretty obvious she had no interest in getting involved.