I also suspect that this chapter might be foreshadowing a rift between Yutaka and Tsumiki: on Page 11 (top panel), Yutaka quotes Tsumiki, observing that "if we [Yutaka and Tsumiki] end up not getting along, we can just go our separate ways"; and on page 17 (top panel), Yutaka cryptically thinks to himself, "I want to be here [with Tsumiki, at Keiki High?], but I also want to run away."
I don't know if the above lines relate to the apparent "flag" on page 18, but I get the feeling that Yutaka is going to screw up his relationship with Tsumiki somehow. Granted, this series is not a drama, so any misunderstanding between them will be resolved within a few chapters. No sense getting too worked up about it.