The author is correct, and I’m sure if they were rewriting their hypervisor from scratch today they would write it in Rust or some other memory safe language, but that’s not realistic. So they can write new code in Rust, but the old memory bugs will still be present, at least for a while.
There’s tons of C/C++ code out there that isn’t realistic to replace. No need to act like the devs are dumb, they know there’s a problem.