I doubt it, due to how the leak is purportedly from 2017/2018 code, and according to the tweet from SteamDB is the version that is included to Source engine licensees.

The original hl2 code leak was a fan from Germany that hacked into Valve's network and stole a version. https://arstechnica.com/gaming/2016/06/what-drove-one-half-l...

There are YouTube channels like VNN that rely on Valve leaks, but most of it seems like running `strings` on their update files. He does claim to have some inside sources, but they mostly seem to provide social commentary on Valve internal politics.