Yeah, I get the feeling it's a red-herring and Kyo is getting himself worked up over nothing. But I won't entirely rule out that Yamada might have hoped for another milestone, yet I often feel like she's not nearly as gutter-headed as Kyo, here, and though I do not doubt she thinks of having sex with him at times, she is nowhere near as likely to think of the sexual ramifications of things, such as her wet, see-thru clothes showing off her racy bikini. Yes, she chose it for him, but she still feels like she's somehow aware that sex is a thing and yet so innocent about it at the same time.
I'll accept it if we get a fade-to-black moment as they end up in the same place with the right conditions, but this manga is still lacking even a 'Suggestive' tag, let alone any of the more extreme ones, so I seriously doubt we'll actually see anything.
And Makeine has the 'Suggestive' tag, same for Cheeky Brat, Duke of Death and his Maid... plenty of ones that sometimes, at best, have only cleavage and the characters getting borderline lewd while clothed (or implied topless states with that weird nipple-less pseudo-censoring). I will admit Cheeky Brat has Yuki Machida go topless sparingly past a certain point, and makes it fairly clear that the her and her boy Shou Naruse are doing it at some point after they've both moved on to college and at least one of them has their own apartment so they can have some privacy... That's still a rating above this which has no 'content rating' tags.
This is deemed 'safe', despite Norio-sensei's sexy extra arts, and even some non-extra arts. She may be a dirty-minded woman drawing middle schoolers, but the manga is still not rated any higher.