I would expect there are other QF FA who are HIV+. I don't know if it is a requirement to declare your status when you join as a cabin crew. The difference in this case (if facts are true) is that the HIV status was discovered/uncovered while in Dubai hence QF can't plead ignorance that this person is breaking the law.
QF are also stuck in a PR rocky hard place because they don't want to be seen as discriminating but they also don't want to declare that they have m/any FAs with HIV for fear of upsetting that ignorant portion of the customer base who think they will "catch" it.