I'm not so sure after rewatching it.
I think the groundwork is being laid to show how Joro isn't really friends with anyone but the book girl. In the two flashbacks Joro gets embarrassed when him and Sun being friends is mentioned. In the instance with the each girl the mention of friendship is what drives him to help them with their respective schemes.
Moving onto the second part of the show, after the Sun's confession we end up seeing a huge miscommunication between Joro and Sun and it's even mentioned how Sun has always seen Joro as speaking in baseball metaphors with him.
This is of course something Joro is oblivious to.
Adding onto this we've seen since the first episode that Joro's inner face(本音 is what i think i want here) is not shown to Sun or Himawari (best friend and childhood friend) but rather to the Book-Stalker girl. I would think that one's inner face would be something to be shared with those you are intimate with; something that Sun is with Joro, but Joro is not with Sun.