I'm really not sure what this article is trying to say (other than what it claims in its title). Seems like it's all over the place and not making any coherent points.
I think it's trying to say that Ashely Madison is used mostly by promiscuous people, and by nature of them being promiscuous, they have had lots of partners and thus know lots of people. Since there are 37 million people involved, it's a good chance that you know someone affected by this hack.