I think that is an artefact Lox.
If you extrapolate the line of best fit back you would reach a zero point aound 1998.
AIDS did exist before that but in that period the numbers were so tiny that trends can not be identified.
If you throw a dice 600 times, you would get very close to 100 sixes.
Throw it 6 times and you could get anything between 0 and 6 hits.