I think your explanation may be correct, but I don't understand why torture would be the intuitive answer even so. First, if I select torture, everyone in the universe gets tortured, which means I get tortured. If instead I select dust speck, I get a dust speck, which is vastly preferable. Second, I would prefer a universe with a bunch of me to one with just me, because I'm pretty awesome so more me is pretty much just better. Basically I just fail to see a downside to the dust speck scenario.