Taro Ase was giving a lame reason just to brush off reporters.
It may be that the Japanese leadership were tipped off that the financial products were toxic.
The US bankers who created and developed these financial products were knowledgeable and experienced. They knew what the toxic products would do to consumers who bought them.
Remember this:
The accumulated billions (or trillions) that Asian consumers lost did not just disappear. The dollar notes were not burnt in a pile.
The money WAS TRANSFERRED from A to B. It is residing in some US financial institutions' accounts now.