I'm glad to see this one was translated! My first thought about what was happening here was that Yurina was writing the manga, but even most self-inserts change the names and stuff to not make it too obvious, so that's probably not what's happening here. Not to mention all of the other stuff that the MC noticed.
Another possibility is that one of Yurina's villains somehow made the comic to expose her identity. Although since the manga has apparently been going on for a while, it hasn't seemed to work.