What, exactly, does distance mean here?

The other explicitly told design consideration for Go was for it to "feel like a dynamically-typed language with statically-typed performance". In other words, the assumption was that Googlers were using C++ for network servers not because of C++, but because something like Python (of which Google was the employer of van Rossum at the time!) was too slow. Go was created to offer something more like Python but with performance more like C++. It was a "C++ replacement" only in the sense that C++ is what Google was using where it was considered the "wrong tool for the job". Keep in mind that Go was created before we knew how to make actually dynamically-typed languages fast.

Putting things into perspective, the distance between C++ and Go is approximately the same as the distance between C++ and Python. Which is a pretty big distance, I'd say. C, C++, and Rust are much closer. They are all trying to do essentially the same thing, with Rust only standing out from the other two thanks to its at-the-time unique memory model. So it is apparent that we still don't understand "gap" to mean the same thing.