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.
You can transfect hTERT into primary lung cells and immortalize them to generate a lung cell line. You can also use iPS to generate a lung cells, then again transfect in hTERT. Hell, you don't even have to do it yourself, you can buy it from the ATCC.
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)
I agree that it isn't an egregious error but it does appear to be sloppy or a bit careless. I guess part of that is hindsight but why wouldn't you want to use cells from the tissue most prone to infection in the disease process? I hope someone is assaying cardiac cells too.