It's just a small bonus animation borrowed from a recent dev log that we threw in at the last second. It shows if you click the moon that appears in the game menu after you finish. You should be able to see it in Ana's last dev log, so you don't have to finish it again 😬
(Ana made a series of small games featuring Sonya and the blackbird years ago. After we connected, recently, we've taken up the story. With all the positive response from this stunt, we now hope to release this as a stand-alone experience (prequel) and eventually complete the full game of Sonya's adventure.)