I don't think they were offering up Go as an alternative to C, but rather giving an example of an OpenSSL implementation in a language that isn't C. Rust is mentioned because the prior comment called for the creation of a pure-Rust OpenSSL library as proof that Rust can be used in this context. No such things exists, but they were trying to offer up a similar example to prove the same point.
This is a false choice. Go and Rust are not replacements for each other. They both have qualities which make each better suited for different environments.
Rust is actually capable of replacing all uses of C, Go's runtime will generally be an impediment to using it in certain cases.
Also I would argue that there are entire classes of bugs that are still available in Go that are not in Rust, that make it less suited for security. Null pointer exceptions, and unchecked errors are the two that come to mind.