Yeah, this is stupid. There haven't been any romantic developments between Chinami and Oguri until now besides Chinami reacting weirdly to him and wondering why that was happening. The story has spent far more time developing the relationship between Chinami and Yuika, which had explicitly involved romantic feelings on both sides, so it's kinda lame to just see it shafted in a three pages.
I get that some of these Japanese authors have a fetish for their guy best friend turning into a girl and falling in love with them, but damn, if that's what you wanted to write then that's what you should have written.