Well, to put it as simply as I can -- sketchy demon boyo (forgot his name, lel) said that Rum wouldn't notice when Ginger opened the cube a little bit and took a peep through his subconscious or whateva and that much may be true. But it almost seemed as though the person they were above seemed bothered by something and I'm inclined to say it had to do with the cube being opened + Rum getting mad at Ginger and asking what he did only makes sense b/c Ginger is the one with the cube. There were clearly other side effects to the cube being opened that sketchy demon boyo didn't explain and I suppose we'll see more of that in the next chapter.
This is precisely what I knew would happen from the fucking beginning. Just call me plot Queen~