Ok sooo, the graphical glitches I was experiencing in the epilogue were not intentional. I kind of suspect it's something specific to the Linux build or maybe I don't have some graphics settings all the way up.
And also, since I mentioned there is "more" which is the _supersecret.rar archive, no, it's not something I could've figured out on my own, but you can look it up online what it's all about. It's just some neat extras, but it was very hard for players to crack the code.