They wouldn’t be exposing anything unless they’re making out in the car in front of the school. They could be two relatives, friends, roommates, whatever...nobody is going to ask unless they provide some reason to ask. And they obviously wanted to stir something up by doing just that.
I understand your point, but disagree. There is no way they could hide that for long. Unless the child was too ashamed or whatever to talk eventually the kid’s...uhmm...unusual family life would be exposed.