It's generally against both C and C++, because the reason applies to both of them. That reason being that using these languages expose users and the world to huge negative externalities in the form of security vulnerabilities, or alternatively (but resulting in the same conclusion) that the speaker just likes writing correct code.

> And it doesn't make sense to use C when Rust does the job.

There are few jobs left where C can do it and Rust can't, those jobs are generally "well there exists a C compiler for this architecture and not a rust/llvm backend". Rust is generally just as capable as C is at writing low level code. If you're willing to put up with translating macros by hand (or using wrapper functions), it's even capable of integrating with existing C code bases.

Lots of people still prefer C over Rust in various situations where you could use Rust, so I don't think it's a generally accepted fact that "it doesn't make sense to use C when Rust does the job".