MarAuthor
I don’t get the confessing he’s from earth bit, unlesss he wants to reveal “your life is manga/anime” but that would likely drive a bigger wedge between them more than what he just did now. Momonga trusts all his “creations”, so what would happen when he finds out someone from EARTH was impersonating/transformed as an NPC? He would close off, he would distrust others, and he would probably lose the little bit of humanity he has left in him because he see’s all his friends within Nazarick’s NPC’s. Sorry for the long comment, I just don’t want to see another fanfic I am enjoying to be ruined by quick “plot twists” and rushed interactions.
Why confess? He did actually nothing bad, just had a little more of proactivity , that could be explain by a better background history(imposible for Momonga to remember it if it was not him his creator) and not being totally fanatic because of that or any other idea that You could put on the background history. He is still loyal. Make mistakes that are common for NPC because he is not a player. This could have been just a repeat of Sebastian to test loyalty that for a more independent NPC would be the star for making him not wanting to serve and perfect excuse why he would not like them in the future
Theory time, what if thot is trying to get away from his library? He spent years in a place that had almost no sound or other stimuli. Also no human interaction at all, any normal human would go crazy. He hates his library but this contradicts his lore, so he makes excuses to leave the library. Such as going to see Aura or trying all different types of search magic to report to Ainz about.