Well, maybe not completely random. Recruiters are generally random and have no qualms about adding people. People also will add people at the company, even if

Well, maybe not completely random. Recruiters are generally random and have no qualms about adding people. People also will add people at the company, even if they don't work together, or even colleague of colleague type connections are pretty standard. Doing so on FB I think would be weird, especially across genders.