@HYBRID_BEING about the room arrangement, it's still possible that one also within the scheme (in a story like this it can happen), but she has the motive and means, and there are things I think might be the clues:
1. idk how famous nikaidou san is, but it seems the "reporter" recognized her well enough even for being underage
2. how the "reporter" know that the glasses guy is her editor, normally it's something ppl only know within workplace group, right
3. ninomiya was there can't be ignored as just a mere coincidence