Did you read the "highlights"? "Fell short of significance at the 24 hour time point, similar to remdesivir" and an SI of 40.4 vs B's 426.
"We found that plitidepsin significantly reduced genomic RNA content at 8 and 12 hours post infection and fell just short of significance at the 24 hour time point, similar to remdesivir treatment."
"...with an IC90 of 3.14 nM and a selectivity index of 40.4...