Don't follow too closely, but I seem to recall some evidence that certain people were just immune to AIDS.
Most healthy people are fairly good at fighting HIV - but since it mutates at a great rate and is hard to eliminate entirely - it will sort of fester in dark, out of the way places in the body mutating until the body gets tired of fighting or it comes up with a form which is far harder to fight.
I believe with the right drugs, it is *usual* to test negative after the initial positive test + drug theropy, but the infection still exists - just not in the tested place (bloodstream?)
I read a few articles on this and the one thing I'd add (not sure if it's in the linked article) is that this guy actually had sex with an infected person after getting his HIV postive test. That is a Bad Idea (tm). Addition of a different strain of HIV could considerably shorten your life expectancy.
I hope this guy holds the cure. Oh god I hope (if you're listening: unicorns and atlantis would be cool, too).
However, I expect he got hit with a form his body was just exceptionally good at fighting. They take blood, HIV +. His bodey fights for a while, he reads HIV-. However, he's still got it somewhere. Lymph system, organs, I don't recall the details. And maybe he'll live a bit longer then most, but eventually he'll get hit with it.