Not a mirror, it was forked initially from that repo 2 years or so ago when the codebase had just roughly 20 commits, and it the contributor graph shows it is indeed basically just Dustin working on this.
I started the project while I was working at Google, went through the open source process, and then left a short while after to work on it full-time. There's no affiliation with Google.
I'm super-curious to hear more about this, in that it's hard to imagine walking away from a significant stable money-stream like Google.
It's a bit more of a story to tell offline. In short, the stable money stream quickly leads to a comfortable savings, giving me time to try an experiment like this. Right now I'm motivated by technically interesting projects that might lead towards good things in the real world, and once I was in a position to realize that, there was no way I wouldn't be working on A/B St.