The open source license allows me to fork the implementation of Go, but not use a derivative of the Go name for my derivative of the Go implementation (to ensure/show, among others, that people know that my work is about Go and not some other language or something i came up with).

Since when has being able to use a derivative of the name ever been a requirement (or important) for free software?

The original toplevel comment was about making a new compiler, not a derivative of an existing one, the comment you reply to is a continuation of that discussion not a standalone comment. The implication here is that the open source license is about a specific implementation and only covers that implementation but it doesn't cover its name, as you rightfully point out. Munificent wrote that the open source license protects you if you decide to create your own Go compiler and name using a derivative of the Go name, but this is wrong since the open source license does not cover the name.