I feel like Valve isn't particularly interesting in making Eps 3 because it doesn't have anything to teach them. There isn't any new updates or work on the Source engine so Valve would be creating a game just for the sake of it which they normally don't do. Usually they want to improve techniques, certain artistry, and add a lot of passion into the game. I am just happy to play Black Mesa Source this year : ).
This bit alone makes it obvious it's not real. It's ITS, not IT'S! Sheesh. Basic fucking spelling and grammar.