What, you don't?

It's not just you; I was also confused at the beginning. Seo Minhye in the present looks pretty similar to Park SooYoung of the past, just a little more slender and younger but not by too much. Add to it the whole fashionable actress concept and the comfortable manner she started talking to MC with, and I say it's pretty normal to get them mixed up.

He's accomplishing a few things with this. First of all, the set up of the dungeon is completely unreasonable even before MC started messing with it. It goes above and beyond what would be considered normal or even sane to get a high score. The other incidents involving the school can be covered up as mere accidents with the proper press coverage, but something like this is very obviously intentional, showcasing the principal's twisted mindset and unfairness towards the students. Furthermore, there are more people who will watch something for entertainment than they would read the news, so this is actually broadcasting this out to them as well.
Second, and perhaps most importantly in this case, is that he's putting himself forward as a banner to rally those who hate the principal to contact and work with him. A lot of people hate the principal, but they're unwilling to do anything because they fear retaliation or don't quite have enough to accomplish it. Get enough people invested, though, and they'll be able to pull him down and stain him with the mud he tried so desperately to avoid. The only thing that's protected him so far was his connections and influence, and that can only go so far when enough people start causing problems.