It's possible of course, but if you compare the two possible scenarios, one seems more likely than the other;

1) Child was infected with HIV twice

2) Groundbreaking never-before-achieved treatment didn't actually work

In the first, something extraordinary (being infected) has to happen twice, in the second, something extraordinary (being cured of HIV) has to simply not happen.

So it seems - on this basic, without-the-facts, examination at least - much more likely to be #2 than #1.