"Care to explain why the Communist party of China has offices inside of Huawei's headquarters?"
Sure. They do that with most large institutions from what I've seen when in China. There's a Party office in all of the universities, too. It allows the Party to keep an eye on things as well as serve as a liaison between the institution and the government when needed. Also, since companies are responsible for handing certain things for their employees that we would not necessarily consider companies doing here in the USA, the Party office helps administer those things as well. It's no huge conspiracy or anything like that. It is just a government that has more direct interaction with people's lives than people in the US would think is normal.
I've been to China many times (mostly to universities) and these Party offices are nothing unusual there.
The idea of "keeping an eye on things" may fit into various conspiracy theories. All I know from my many trips to China about those Party offices is what I've been told by my fellow professors, by the graduate students I taught, and by my friends and colleagues over there.