My personal theory? He's aware of Fuko's feelings for Mika, and he doesn't really disapprove. But Fuko is in an arranged marriage. (Also he was telling her to walk Mika home. xD) This one kind of ties into him apologizing last page. I have 2 other theories to xD Mom and dad are split / mom is dead. and Dad wants Fuko to visit(possibly with Mika)
That's my personal thoughts =P
As for eavesdropping, it's not as if she was sneaking around.
She walked up and they happened to be talking. So she just happened to catch the back half of their conversation. Which is completely irrelevant without context, and not exactly eavesdropping.
I would assume she's about to call out for Fuko, or Fuko is about to see her anyway.