I feel we are pretty much derailing the thread at this point; sorry for people who are just reading along 
At the same time, I’m really happy to have this discussion. Maybe we should move soonish to, say, the マイン main thread 
Anyway, spoilers
So, it is mentioned at some point that you need a ridiculous amount of magic to be able to do that (or, I guess, enough control over it to just concentrate what you have in your eyes). Apparently, [volume 8-ish spoiler?]low ranking nobles would really be hard pressed to do that. At the same time, [volume 7 spoiler]any 身食い with more magic than that would just die very young, i.e. before they can interact with the world. ディルク is around 中級 and without help he would not survive for long. マイン only managed to survive because she learned by herself a crazy efficient may to compress magic.
So, yes, I also assume it’s something that can naturally occur, but 平民 have a vanishingly low probability of coming across it, I think.
About compartmentalization, that’s true as well, but I think the most weird thing about her is when she does something that involves books rather than how she behaves in different contexts. Randomly spouting nonsensical words is a sign of dementia in our world too…