Miharu's boobs is clearly bigger than Sensei's. They are ginormous. Probably the biggest in all of Tsuya's works tbh. So she really is the mom from Tatoeba. I guess she's fine with showing off her body to strange, cute younger boys. Seeing as Miharu historically has affinity for them, it makes sense and I'm sure her son/husband (LOL) wouldn't mind much either.
I wish we could've seen some sexual interaction between them at least, I wish he had the balls to take her up on her offer and join her naked in the outdoor bath and maybe we would've seen some boner/sexy shenanigans, but alas.