It's a contrived type confusion bug. It reads 42h because that address is hardcoded, and it does something that ordinary code doesn't do.
If you were engaged to do a software security assessment for an established firm that used Go (or Python, or any of the other mainstream languages that do shared-memory concurrency and don't have Rust's type system), and you said "this code is memory-unsafe", showing them this example, you would not be taken seriously.
If people want to make PLT arguments about Rust's correctness advantages, I will step out of the way and let them do that. But this article makes a security claim, and that claim is in the practical sense false.
If you were engaged to do a software security assessment for an established firm that used Go (or Python, or any of the other mainstream languages that do shared-memory concurrency and don't have Rust's type system), and you said "this code is memory-unsafe", showing them this example, you would not be taken seriously.
If people want to make PLT arguments about Rust's correctness advantages, I will step out of the way and let them do that. But this article makes a security claim, and that claim is in the practical sense false.