The current patreon release/next public update adds several choices and new chapters to Day 5 which make the scene in question entirely optional and allow the day to end in several different ways. There'll be a number of optional scenes like this in the completed route, though some will impact what endings are available to you. This particular one has no impact either way.
As for how Adrian pulled that off... furry buttholes are magical portals leading to a distant and very spacious realm of possibilities!