I obviously don't know if this applies for the Fil-C bugs but what we saw in Rust is that there's plenty of "technically that's not OK" which is very distant from "this will actually cause real world problems" https://forge-blog.github.io/posts/rust-std-memory-safety/
For example it's definitely not OK that you can impl Pattern in a way that causes non-UTF8 data in a string with safe code. But you probably didn't let random attackers impl Pattern, on a nightly Rust where that's even possible, and so that's not going to cause problems in our real world - even though it's wrong and must be fixed.
I'm speculating out on a limb here, but maybe the Mythos zero-days that were developed into working exploits involved a few of those "usually won't cause real-world problems" happenstances.
A model with all the world's knowledge might know exactly how to weave them together into a successful exploit. And if tomorrow's models are even more capable, perhaps what we're experiencing now is just a fire drill for what's coming.
Most of the bugs were things that fall into the “won’t cause real world problems” category.
But they were all things that unambiguously violated the Fil-C promise