It's a good reason to choose Rust over C++ for that application, and others that share its characteristics. (Or, more to the point of the article, it's a good reason to declare that Rust is faster than C++ for that application.)

It doesn't provide a lot of evidence in either direction for the rest of the vast space of potential programs.

(Knowing C++ fairly well and Rust not very well, I have Opinions, but they are not very well-informed opinions. They roughly boil down to: Rust is generally better for most programs, largely due to cargo not Rust, but C++ is better for more exploratory programming where you're going to be frequently reworking things as you go. Small changes ripple out across the codebase much more with Rust than C++ in my [limited] experience, and as a result the percentage of programming time spent fixing things up is substantially higher with Rust.)