They were sitting in the middle of a packed conference hall. It was not a private conversation.
I have been to many conferences, and have, many times, told something to someone that I thought might have been funny. While I don't think I have ever said something that I would think was harmful I nonetheless have said things that I would be embarrassed of they went "public", because I simply would not have wanted to be the focus of the attention.
I have read Adrian's blogpost, and she doesn't give enough detail for me to know just what it was about the comments that was offensive. Whether they were or not, I don't think it's unreasonable to expect that the two developers were expecting their conversation to be quasi-private.