Thank you so much for the comment!!
I did think about that while writing it - it's not very clear in the story, but the idea would be that the monster world and the human world are having a class in the same room at the same time, but MC can see the monsters (and possibly can't see some or all of the humans.) The professor could be the monster one or the human one - this is something I'd like to clear up and expand on in a future update, I just didn't have time before the deadline. Sorry I can't do a better job of answering your question right now, but thank you for asking!
I'm also so happy that you like Nikolai!!! I was a bit worried about him, I confess! He's certainly not everyone's cup of tea, haha!