Maybe no one in that specific company really knew the language, but there's loads of people actually using the language, it's not like it dropped from the clear blue sky. It's not like there's a Rust salesperson that knocked on their door with a leaflet. They're not even the first persons to write a database engine in Rust.
I wonder if other engineering domains have this same silliness. Do the architects have intense debates over steel H beams vs wooden LVL beams, and at some point newbie architects believe you should only switch from one to the other as an architecture firm if your architects have experience with it, because the only way to know if it would work is reading the marketing claims.
A compiler is just a tool. If you're doing a rewrite you better pick your tools correctly, and it seems like they did. You could theorise they were lucky somehow, or you could recognise that they're experienced, educated and skilled and made the right choice based on their researched.