Yes, in a way LR and you are correct. 97% reduction was achieved when compared to what happened in comparator culture left untreated, in other words, treated with nothing. However, it does not follow that substance with marked viral load reduction vs. 'nothing' would lack potency, one measure of which just happens to be viral load reduction.
"I would rather have questions that can't be answered than answers that can't be questioned." Richard P. Feynman