I think Rust is a great language, but I think it shines in contexts where you'd previously have used C or C++. Web apps aren't really one of those contexts, unless they're microservices with extreme performance requirements, and this isn't the case here. Why would one choose to write something like this in Rust over easier-to-write languages like Go?
Can't speak for the author, but I'd choose Rust over Go/Java/Python for such projects for following reason:
* Rust is a more pleasant language to work with, i.e. Sum type, pattern matching, and Drop trait closing resources/cancelling tasks.
* Type system is much more robust than Go and Java, resulting in better quality code with less requirement of unit tests.
* I don't care about performance much (for personal projects), but a free performance is always a win.
I think people already exposed to Hindley-Milner will find Rust far more tolerable and productive than Go.