Well, they're the largest non-US-govt owner, including $150B more than US households. I'm not sure the Treasury and Social Security Trust count as far as external influencers, so China is still at the top of the pile, despite only owning 8%.
Given the current debt ceiling situation, I think it's more likely this breakdown is being presented as an answer to the question "who suffers if we default?" rather than "how reliant are we on external influences?"
