Go was born into 64-bit era, I remember seeing many more bugs that only occur on 32-bit systems. I'm pretty certain the observation in the article is correct that no one at Google tests Go on anything apart from 64-bit ARM/x86 Linux
You can see a list here:
(That particular build dashboard just shows post-commit tests. '386' there is 32-bit x86, 'arm' is 32-bit ARM.)
I can't speak to what Google runs in production or what Google tests internally, but the Google-run CI for the Go project definitely does test 32-bit, and those tests essentially match the tests run against 64-bit.