Yeah, I was wondering why this was being announced on Square's website. Seems it's because Square happens to employ Soutaro Matsumoto, who wrote the post and is also the creator of Steep[0] (an implementation of a typechecker for RBS files).
It's not clear to me whether Soutaro is a member of the Ruby core team, so it feels a bit odd that the post is written like an announcement from the Ruby maintainers.