And? The point is not what they did, the point is that Miharu said that she happened to see Nozaki in the street and that was enough for him to bring up if it bothers him or not.
Change the persons so, imagine a compromised woman that gets a message from her male client wanting to meet at the middle of the night, meeting up he invites her to a hotel, they get inside, the man showers and ask her if she will not shower too, talking with her in only a robe, but the man has a mental breakdown and nothing happens at the end.
After that the compromised woman's man meets a woman friend of his at random in the street, they talk and he goes home, hearing that the woman says "you meeting with other women bugs me a bit..."
Which man would say "well, nothing happened so..."
It's simple logic, don't do to others what you don't want others to do to you.
He shouldn't have meet with a client outside a professional place in the first place, and should have bailed the moment she hinted at a hotel let alone take a shower.