Author here: my sibling already explained the language, but I specifically chose "cancer" because I remember seeing the UNIX-haters handbook use that phrase (I'm not exactly a UNIX hater, but it's always stuck with me). I write C and C++ professionally (and I like it that way!), and I think it's perfectly fair and accurate to refer to their spread as cancerous.
> The implied replacement is Rust.
No. Rust was an example. The replacement is any memory-safe language; Rust just happens to have done a great job getting much of the tooling right from the get-go.