Facebook's design team writes about product design decisions, including Reactions, the News Feed, design critique and VR work.
HN links it mainly for the Reactions design process post, and commenters note it shows Facebook employees do blog personally.
Relatively sure they didn't follow as thorough a design process as Facebook did: https://medium.com/facebook-design/reactions-not-everything-in-life-is-likable-5c403de72a3f#.5p49fvc6g
Ok, well, if this is really some big ploy by Facebook to now allow their employees to have personal blogs, then why do so many exist?
https://medium.com/facebook-design
https://medium.com/facebook-design/reactions-not-everything-in-life-is-likable-5c403de72a3f#.iu6yw8x12