A fair point, though the few security issues in recent years I've looked at were not the kind of thing you would turn to unsafe rust for. But I've certainly not done a broad enough sampling to say what % of cases are like that.
To be fair, I am sure Rust catches a fair amount (compared to C++ which would catch 0). I just think that phrasing rust has having 0 memory errors can be a tad inaccurate.