The issue was that the sexual joke - a subtle and not particularly harmful one - was part of a private conversation between the two men. Richards inserted herself into that situation and made a big deal out of it. OK, you could say, she felt upset at their language, so maybe reporting it to the conference organizers was fine. But sic'ing her twitter mob on the men essentially invited the backlash that followed.
Is private the right word? I don't think they were trying to share their conversation with the rest of the room, but they also didn't go very far in trying to keep it from the rest of the room.
In a legal sense, private more or less goes out the window when you share something with a third party, a court would be unlikely to step in and protect the privacy of a conversation held in a shared space.
The internet conversation certainly doesn't have to use the legal definition, but "private" does sort of invoke the idea that the communication is intentionally being held close, and if you are talking in a room with other people, you aren't working very hard at that.
Well, "private" in the sense that it was two people speaking one-on-one in a personal conversation, and not attempting to gain the attention of others in the area.
Obviously not "private" in the sense that they were attempting to keep their communications confidential.
