HIV triggers pathogenesis leading to an onset of AIDS (Therefore, answer for the above question is yes, it is HIV)
Fast mutation rates of HIV cannot always explain the lack of AIDS, since an identical (or similar) HIV cannot cause an onset of AIDS in certain individuals (in this case, it is not HIV)
An individual with a homozygous mutation of CCR5 (CCR5D32 ) is not susceptible to AIDS even with a higher titer of HIV in an individual (no, it is not HIV)
When HST is infected and depleted by HIV, it will lead to an onset of AIDS. However, as long as HST is spared by a depletion mediated by HIV or reconstituted by HST with a homozygous mutant form (CCR5D32 ), there will be no AIDS (again, it is an immune system which plays a critical role of getting AIDS, especially of an availability of HST).
But it all starts from HIV infection (yes, it is HIV)