Do they mean the sort of stigma that manifests itself in an unwillingness to hook up?
Yep.
This is a big "problem" on queer "dating" sites and queer bars, and has been roundly condemned while trying not to shame the ones who want to be careful. Descriptions of advertising dates as "safe" and "clean" do not go over well for the infected, especially when it is accompanied by "you be, too." Trepidation in getting involved with someone who is infected but claims to be "safe" is condemned as stigma.
Another point of contention is the PrEP issue. Those on PrEP (to prevent HIV infection in themselves) are often referred to as "Truvada whores," suggesting that they can have all the promiscuous bareback "sex" they want without worrying about contracting AIDS.
Those are dilemmas I'll get my popcorn out to watch.