The point of my comment is that in my experience, incompetently written, overly-cautious code tends to be more safe at the expense of maintainability and/or performance.
Sadly, I don't know rustlang, so I can't tell if the inability to describe its features in more commonly used terms is due to incompetence or the features being irrelevant to this discussion (see the title of the thread).
The thing is you aren't really asking about a "feature" of rust (as the word is used in the title of the thread), unless that feature is "the absence of data races" or "memory safety" which I think are both well defined terms† and which rust has. Rather you're asking how those features were implemented, and the answer is through a coherent design across all the different features of rust that maintains the properties.
As near as I can tell to give you the answer you're looking for I'd have to explain the majority of rust to you. How traits work, and auto traits, and unsafe trait impls, and ownership, and the borrow checker, and for it to make sense as a practical thing interior mutability, and then I could point you at the standard library concepts of Send and Sync which someone mentioned above and they would actually make sense, and then I could give some examples of how everything comes together to enable memory safe, efficient, and ergonomic, threading primitives.
But this would no longer be a discussion about a rust language feature, but a tutorial on rust in general. Because to properly understand how the primitives that allow rust to build safe abstractions work, you need to understand most of rust.
Send and Sync (mentioned up thread) while being useful search terms, are some of the last things in a reasonable rust curriculum, not the first. I could quickly explain them to someone who already knew rust, and hadn't used them (or threads) at all, because they're simple once you have the foundation of "how the rest of rust works". Skipping the foundation doesn't make sense.
† "Memory safety" was admittedly possibly popularized by rust, but is equivalent to "the absence of undefined behaviour" which should be understandable to any C programmer.
> The point of my comment is that in my experience, incompetently written, overly-cautious code tends to be more safe at the expense of maintainability and/or performance
Well, yes, but that's the whole value of Rust: you don't need to use these overly-cautious defensive constructs, (at least not to prevent data races), because the language prevents them for you automatically.
Sadly, I don't know rustlang, so I can't tell if the inability to describe its features in more commonly used terms is due to incompetence or the features being irrelevant to this discussion (see the title of the thread).