First, consider the difference between the old USSR's stockpile in the 60's-80's and the handful of barely functional devices Crazy Kim III owns. Threats without the capability of backing them up are useless.
Seconds, consider that unlike a nuclear exchange, where once one side fires, the other has no choice but to "use it or lose it", so will retaliate, the rest of the world doesn't hold any significant amounts of Chinese debt or money. So, China can cause anything from a small warning ripple in the currency markets to an unpredictably huge tidal wave in financial markets with little fear of direct retaliation.
Previously, China would have been incredibly unlikely to do more than small ripples, due to the linkage of the Chinese, US, and EU economies. Although Chinese banks were uninvolved in the 2008 near-failure of the western banking system, China took a big economic hit from fewer orders being placed. The people at the top learned from this. As Chinese internal consumption of factory goods grows and as their export markets and raw materials suppliers diversify (check your own note about Africa above), the Chinese economy becomes less vulnerable to the economic fallout that a failure of the US or EU economy would trigger.
Even if China doesn't ever use a "currency bomb", the steps towards independent economic sufficiency is a very wise move. The EU is in another round of crisis over Greece and the US keeps piling on over a trillion of new debt every year. Both situations are further destabilizing the currencies and economies of the west. Of course, as the western economies do this to themselves, they become more vulnerable to all forms of economic pressure as China's economy continues to grow.