re: A Chinese Belgian Waffle?

As Russian has quoted its good for diversification, but the primary benefit of this was simply operational efficiency.

When you have a segregated account at a clearinghouse, it becomes much easier to post collateral and settle transactions compared to if the PBoC had to post and/or hypothecate collateral back and forth from mainland China or their outsourced managers to a clearinghouse. It cuts out a step that can sometimes be a pain in the arse, and allows China a good relationship with the European clearinghouse. From there it becomes easier operationally if they want to trade anything with Europe or the US. If the question is "why Treasuries?", that's because US Treasuries are far and away the primary source of collateral globally with the smallest haircuts across the board.