This somehow confirm the theory uncle replay things from the "cloud" and not from his own memories, because he erased that memory ( after writing it in his notebook) and still is able to access it.
About tsunderelf, I don't think we will see her in uncle world unless she reincarnated there, and this somehow related to that very high level resurrection spell uncle mentioned in previous chapters.
Uncle talking to spirits is not new, as been show from time to time before we know about his cheat skill.