tl;dr: A Valve employee in 2016 told Tyler about a few things Valve was working on. Tyler kept the chat log and shared it with friends. Unrelatedly, TF2 and CSGO's code was semi-publicly leaked in 2018, and one of the friends found and held onto that. Tyler and the friends worked on a fan project together named F-Stop, after an unreleased Valve project, but then one of the friends had a falling out with the rest of them and published this stuff together, probably to embarrass him for sharing the chat log and maybe to make him look involved in the TF2/CSGO leak.
Refer to this r/Games thread for more details: https://reddit.com/r/Games/comments/g61v4x/_/fo6r9ef/?contex...