They have been increasing their footprint in Central Africa for years and already have secure routes from the Middle East and Russia (both crude related, but the latter can help with rare metals).
They have been agitating waters in the China Sea for years as well and now with BO in for four years, this stockpiling would indicate an attempt at a landing from the US which will never happen and if BO has his way then the 7th Fleet becomes a non factor in the Straits.
With hard assets in Africa and Australia, coming assets in Canada and buddy-buddy relationship with former enemy Russia, then we all have cause for concern.
I don't believe the stockpiling is the reason as much as it is a by product.
But I see where you are coming from and this is just my opinion.
Taking everything into consideration, I see this large increase in China's stockpiling of commodities as indicating a likely escalation in tensions.