It's healthy to have a normal amount of cynicism. They released it for a reason. "The goal of our open source endeavor is to provide full transparency to you, our users, about how our systems work."

Why be transparent (or try to appear transparent)? To convince people to trust your platform (or to recruit - which seems to be another goal of the post). Why would Twitter want or need to do this now? Well, there is a bit of context. This disclosure doesn't exist in a vacuum.