In their defence, rust is alright to spin up simple APIs or even complex backends. It wouldn't take me more than a few hours to write a small graphql api in rust.
If they decided to write an API in rust just because, chances are it's not anything important (I hope). From their post, it seems like lack of familiarity is the core issue.
There has been a movement in the Rust community to position it as good for backend web development. This is why there's been so much work on async, excitement about Actix, etc. It's not hugely surprising that this has given outsiders the impression that Rust might be a good choice for backend web development.
The reasons for this movement escape me. We already have many good options for backend web development. None of Rust's unique strengths offer any advantages for it. Focus on web has diverted effort from areas where Rust could really make a difference, like embedded, drivers, and desktop.
The best i can come up with is that a lot of people have come into Rust from other languages where web development is a big deal (eg Ruby), and it's just impossible for them to imagine that a language could be good and successful without winning at web development.
If they decided to write an API in rust just because, chances are it's not anything important (I hope). From their post, it seems like lack of familiarity is the core issue.