This has nothing to do with Rust itself. While the compiler does prevent a lot of common pitfalls, you can still write erroneous code with it.
It's entirely the rustler project's effort (and goal) to wrap any kind of Rust program so that it will not bring down the BEAM under any circumstance, which they have done a great job achieving.
It's still to a large degree Rust itself. It's the language design which makes it possible to wrap the NIF C API in a safe fashion (e.g. using lifetimes, phantom data, etc.). The only additional safety feature we use is catch_unwind (https://doc.rust-lang.org/std/panic/fn.catch_unwind.html) to prevent panics from unwinding into the BEAM (and killing it).
