That, or, not completely unlikely, he was shown all the vulnerabilities across all old software that banking, finance et al use daily and are unlikely to ever update. I am only half joking. There is a reason I think some people should stick to their areas of expertise.
It currently works because those vulnerabilities are not exploited en masse. With AI, they can. It does change the game.
I am personally of several minds about it. However, I am not an expert in the field. I can somewhat reliably opine on humans and human behavior in general, but I concede that is harder to consider the impact in aggregate.