Well, it was said in the post, there were women touching women. And said in the comments, there were men being touched as well. Also, there is an edit to the post, saying that after the initial bit, no one not wearing one or the other button was asked at all, for reasons of avoiding creepiness, so that takes care, I think, of the people who aren't interested being involved aspect. I suspect it's called the open source boob project because breasts are socially seen as an especially desirable yet prohibited object, and so they were what the project started with.