Well, they might not fool you or me, or swiss customs agents, but if they may be able to fool someone - that’s the idea. Pledge bogus securities as collateral, and borrow legitimate currencies/credit.
I cannot see an entity taking bonds demoniated at a minimum of 500,000,000 from a couple of guys alleged to be from who knows where and not verifying them. If the amount shown to any one prospective party were big enough, it would mean only japan china and UK could be the source of the bonds.
Something is very wrong with the story elements known so far, but we may never know the truth. The guys were released. They were not charged, etc.