Yea I just think of normality. If we had h2so4 and were calculating how much naoh to equal the concentration in nM1V1, we would use a normality of 2 for the h2so4. Not sure if this thinking process is correct, but it makes sense to me (dissociate more than 1 H so more than 1 acid or something like that).
Notice that in the question they did not use the word "Conjugate" in any of the answers. This is really important.
HSO4 is indeed the "conjugate base" of H2SO4. However, removing its relevancy from H2SO4, and observing HSO4 on its own, it must be considered an acid, (a weak acid at that) since it has a H to donate which will partially dissociate in an aqueous solution, just as the answer describes. That's the property of an acid, not a base.