My time writing trading software was never on the automated end of things, so I'm only modestly qualified to comment. But if I were doing the post-mortem on this one, the first thing I'd look for is middle management time pressure forcing a large release without adequate testing. And my standard for "adequate testing" would be pretty high.
If you're going to release something that can take down the company, it's worth making sure it works. In this case, they lost circa 400x the lifetime median income of a US worker. It's hard to imagine the upside that would have justified that kind of risk.
