it is pretty astonishing to me they they wouldn't be using lung cells for cell culture experiments. Give the Sars-COV-2 effects on heart, one would like to see some kind of a cardiac muscle cells being examined as well.
culturing cells in vitro - let alone establishing good models to assess an antiviral in those cells - is very difficult, which is why using established cell lines is often done. So I don't think this was any egregious error or anything, but certainly the results should have been taken with the appropriate contextual limitations (and in this case a drug aimed more at blocking viral entry in particular may not have been optimal)