Nature link says the drug targets RdRp specifically which is a type of RNA copying mechanism (mostly?) confined to viruses. Wikipedia says about RdRp:
> RdRps can be used as drug targets for viral pathogens as their function is not necessary for eukaryotic survival. By inhibiting RNA-dependent RNA polymerase function, new RNAs cannot be replicated from an RNA template strand, however, DNA-dependent RNA polymerase will remain functional.
> RdRps can be used as drug targets for viral pathogens as their function is not necessary for eukaryotic survival. By inhibiting RNA-dependent RNA polymerase function, new RNAs cannot be replicated from an RNA template strand, however, DNA-dependent RNA polymerase will remain functional.