The problem is that "fork" means two different things at this point. Compare "FFmpeg developers fork FFmpeg" in the sense of "...and create libav" and in the sense of "...so they can submit pull requests." One is extremely newsworthy, one is extremely not. If you're posting something to HN, it's a reasonable assumption that readers will think you're posting a newsworthy thing as opposed to not.
How do you know the intention of a fork without their own explanation? It was unknown at the point of posting, and posting title is still technically valid.
This posting let you know their intention. Isn't it newsworthy?
"Google employees are contributing to another project" is not newsworthy, no. Neither is them creating a github fork unless you have evidence that they do not intend to use the fork for the main reason people create GitHub forks: contributing.
