The Liu Xiaobo case shows that (some) other countries see the Nobel committee as an unofficial extension of the Norwegian government. If China thought that the Nobel prize was handed out by 6 random dudes in some private club then the Nobel prize probably wouldn't have had such an impact on the relations between the Chinese and Norwegian governments.

Or perhaps China is trying to pressurize the Norwegian government into removing independence from committee, as well as warning other countries not to do anything similar.