Eh? They didn't/aren't using their stockpiles to anywhere near the extent the US has! There reserves are much bigger - they have about a years supply - yet they used less in absolute terms than the US!
What they did was aggressively reduce demand by accelerating the switch to EV's and firing up a few more coal powerstations.
In terms of influencing the midterms - I suspect China isn't anywhere near the front of the queue in hoping Trump get's a beating given the chaos he is causing.
Complaining about foreign interference is ironically straight from the Hillary playbook.
They are strategically using their stockpiles. There are a lot of factors in their strategy and some of them conflict. This has an effect on the world market.
How much of their strategy is to change elections vs other concerns I don't know.
Frankly if I was China, I'd be conflicted about the mid-terms - Trump is currently leading the US to disastrous wars - kinetic and trade, pissing off his closest allies, under-mining the dollar, and making China look a sane and stable partner.
On the other hand the world might be better off if he was more constrained post mid-terms.
Frankly, in terms of countries wanting Trump to take a beating in the mid-terms, I'd put countries like Canada and most of Europe way ahead of China there.
And in terms of China's energy strategy - China is the worlds biggest net importer of crude therefore China's strategy is going to be focussed on managing that first and foremost.
I think it's the US who hoped that the oil crisis would impact China much more - this is the US making, not China.
