Why would you think that? Bugs exist in complex software no matter how hard you try, including software written in Rust such as the Rust compiler and standard library. Did you expect the highly competent people working on these projects to just one-shot everything?
You may have noticed the wave of "rewritten in rust" software in recent years, whose only (?) selling point was that this makes the software somehow automatically safe and if not bug free then at least significantly lower on bugs.
This finding is just yet another nail in the coffin of that myth.