You're right, Chiu is probably the only one who would pick up that there's something WRONG with the scenario where one of her classmates who looks ten is somehow the mother of her 15 year old teacher.
I also think that as a result Ayaka is likely to be the only student not chasing after him.
And Chachamaru's crush on him is going to be interesting now, isn't it? He now qualifies has her half brother, maybe