C existed before Rust; before Rust it was my favorite language, though I rarely chose it for work b/c of safety.
The strongest argument in this piece is that Curl is written in the most portable language available. That's a great reason! And it's been a wildly successful project! Kudos to the developer(s)!
The only problem with this piece is the claim on what are logic bugs vs. C bugs; but that should not detract from an excellent project. The real question being debated is this: if starting a new project like this, should you do it in a safe language to guard against security issues, or should you do it in the oldest most portable language ever.
I'd argue that by the time any project becomes successful after being written in Rust, the LLVM (and Rust) will probably close that portability gap.