Only because that was the terminology used on the Github readme. He was quoting it verbatim rather than asking what environmental variables needed setting. The reason I think this is because he also went on to say "I thought one of golang's selling points was the fact that it created a simple binary." which relates directly to discussions people make about JIT compiled (eg Python, Javascript, etc) vs AOT compiled (eg C++ and Go).
It's also worth noting that you're only specifically discussing environmental variables, where as a development environment is more than just that. Aside having your build tools in PATH (and lets not forget that gcc and make need this just as much as go does), you need supporting shells for the ./config(ure) scripts, any source libraries for C++ includes, and so forth. So you could equally use the same "working [language] environment" terminology to describe C++ - or in fact any other programming language too.
Which is why I think he was asking why he needed Go installed to begin with.
It's also worth noting that you're only specifically discussing environmental variables, where as a development environment is more than just that. Aside having your build tools in PATH (and lets not forget that gcc and make need this just as much as go does), you need supporting shells for the ./config(ure) scripts, any source libraries for C++ includes, and so forth. So you could equally use the same "working [language] environment" terminology to describe C++ - or in fact any other programming language too.
Which is why I think he was asking why he needed Go installed to begin with.