I think it's a combination of evangelism and excitement but also of a fallacy, thinking that a Rust application ought to be faster and more efficient with system resources, so people "helpfully" inform of this.

As any developer knows, a low level programming language may help you get there, but ultimately this is mostly dependent on code quality. Rust applications can be absolutely riddled with bugs and use O(n^2) algorithms where they don't need to, or have awesome code but rely on third party libraries that don't. There's just so much surrounding the core aspects of the language that we just can't judge applications based on their programming language.

Rust does protect against buffer overflows and pointer misuse etc but so does many other languages nowadays, for example by directing the developer away from (or not even supporting) the use of low level unchecked pointers in the first place.