Rust does not solve the memory safety issue. It does mitigate it, and the post is about mitigation. That study finds that Rust "successfully limits memory-safety risks to the realm of unsafe code".
It also finds that Rust has novel patterns of unsafety in unsafe code. That's important! But it's fully compatible with the claim that Rust is much safer than C overall.
I don't think it ever says that the sum of safety in safe code and novel unsafety in unsafe code adds up to as much unsafety as C. The paper's overarching claims aren't quantitative.
I think you're overstating the claims of both the blog post and the study.
It also finds that Rust has novel patterns of unsafety in unsafe code. That's important! But it's fully compatible with the claim that Rust is much safer than C overall.
I don't think it ever says that the sum of safety in safe code and novel unsafety in unsafe code adds up to as much unsafety as C. The paper's overarching claims aren't quantitative.
I think you're overstating the claims of both the blog post and the study.