That is not what China’s non-interference policy does or is about. China’s NI policy isn’t strictly regarding the internal politics of sovereign states, in that China doesn’t care how everyone rules their own house, and would not seek to actively encourage dissent and help ferment unrest.
China’s NI policy in no way limits China’s ability to respond to requests for aid from other countries, which include military aid.
The Korean War is a clear example, as is the Vietnam war, although to a much lesser extend since Chinese activities were clandestine.
Although the Sino-Vietnam war would be another good example of Chinese direct military intervention in aid of an ally in Cambodia as much as it was about punitive action against Vietnam.
China just doesn’t make a habit of constantly going on foreign military adventures like western governments, indeed China actively goes out of its way to try to have good relations with everyone and not to pick sides. The Middle East would be a perfect example where China has great relations with Israel, Saudi Arabia and Iran.
You do make a good point that China doesn’t get the respect it’s power deserves a lot of the time due to its restraint and peaceful approach to international relations.
But that is a double edged sword, as if China does really show its military capabilities, and engage in hard nosed Great Game direct competition with the US-led west, it will effectively kick off a new Cold War.
China wasn’t to avoid that, or at least delay it for as long as possible. As such it is willing to take some small insignificant losses in the meantime.
