I'm not sure that China being powerful was the sole reason flights were not stopped. I think also that the number of people travelling each day between China and the rest of the world is vastly more than the number of people travelling between Dem Rep Congo and the rest of the world. Wuhan had non-stop flights to Heathrow - nowhere in DRC has direct flights to the UK
There was simply too much economic activity between China and the rest of the world and too much money involved spread over different people for Govt, airlines and corporations around the world to agree voluntarily amongst themselves of the need to close all the links
I agree with LTNman though - had something nasty appeared in Lubumbashi (2nd city in DRC, 2 million urban residents), nobody would have thought twice about closing DRC off from the rest of the world - and even companies sourcing various mined minerals would have known to just keep quiet