The most impressive part is that they’re able to discuss CS stuff in Chinese… My college roomies in my CS days were from my country as well and were TA’s and it took all of 30 seconds to switch in English simply the terminology did not make any sense in our native language… This was my experience with most any foreign student group back then… (how do you say null pointer in Arabic? good luck with that 
)
I would bring it up to the prof’s attention for a couple reasons, but mostly the waiting time. If you’re in line and did not ask a question or participate directly to the conversation I’m not sure what the prof can do about it; Even if the door is open, as long as you’re not part of the conversation, it doesn’t matter.