No-one's acting particularly human this chapter. They seem to be acting out-of-character just so that we can have a silly pretend-to-be-dating premise happen. A trope that is ridiculous already on its own, but even more so considering the characters that have to pull it off.
Hinohara, in attempt to cover her tracks, agrees to an absurd deal that she shouldn't even have any authority to agree to. Her behaviour is simply strange in isolation, but, ironically, this would implicate her if other clues of her love for Nagai come out. If she were to ask herself "What would a teacher not in love with their student do when hearing this proposal?" she might just realise they would call it out for the ridiculous thing it is.
Nagai just somehow relents and accepts the whole pretend-to-be-dating deal. I can only reason this is done offscreen, because he wouldn't actually accept.
Then there's a whole host of bad lessons in this chapter.
- "You want to focus on singing/studying, so date (or pretend to, same thing really) this girl so that the other girls will keep it in their pants." We need to move away from the idea that it's open season if you're not with someone. If you don't want to be bothered by some jerk who wants to try out some pick-up lines, you shouldn't need to be in an existing relationship. The message is all wrong.
- I get the people at this camp are going through puberty 'n all, but the reasoning that girls would end up fawning all over him, and are just lacking the capability of restraint by default is insulting.
- Then there's the scene where Aizawa pushes him on the bed, and when he pushes her away starts pouting. Can we not make attempted sexual assault rosy/cutesy/flowery? What she did there was messed up. There is nothing wrong with having this in a story of people going through a phase in their life where they still need to figure this stuff out, but the presentation is everything. Had she had more strength than him this would not have remained at a mere attempt. I can't help but keep asking myself the question "Would the author have written things the same way if everyone's gender were reversed?"
"I won't interfere, boss." You're a grown adult, respecting a proposal that can only be seen as childish and speaking to a teenager as if they're your equal. You look silly.