4x. The crux is that they can flip a switch to change global oil supply, be highly resistant to embargos, and are no longer subject to OPEC (through Iran & Russian oil traded in Yuan). They can now change global oil prices at will and resist attacks on their energy imports.

Which makes sense. The US is a net oil exporter -- in a strategic emergency the US will still have access to oil. China will want to have a much larger buffer, since its economy requires oil from other countries.

They were also able to drastically cut their own internal demand and external sales/shipments (the article mentions jet fuel to other Asian nations).

This was possible because their economic planning is centralized.