Pity they choose "Golang" instead of "Go" for their default Go image. It's called "Go". And they built Docker with Go.
This is like the new "It's GNU/Linux - NOT LINUX!" Except with less validity. It's totally interchangeable in common usage, and in fact much more explicit to use the term "golang".
That's why they know "Go" is very often called "Golang", for search-engine-related reasons.