I'll agree that it's possible to just keep shooting with digital, indeed it has been called the ultimate in hit and miss photography.
The cost is something that is often misquoted as most comparisons are unequeal. To actually print up your digital shots would be very very expensive, most are content to stick them on their computer and leave it at that. Shoting a roll or so a fortnight of film then the economys of digital don't really come into play , it's pros and serious amatures where the costs become apparent. Has our martian friend already got a film SLR? If so then the cost of a DSLR would buy a lot of film for it.
As to it being or not being art, that's very subjective. I'll agree most isn't but the tools be they a camera , paint and brushes or hammer and chisel are really only a small part of artisty, imagination and vision are 99% of it. And just because a picture is painted doesn't make it art either. Go to any statley home and you will see wall after wall of paintings of the first earl , second earl , third earl and on and on, not art just representations , and then there's all the modern stuff, you know a black canvas with a few streaks of yellow down it and a four figure price tag.
I feel the art comes from actually convincing people that it IS art and charging them that four figure price tag
Anyway here's one for you ,an exhibition of photography at the V&A museum. Photography but no cameras.
http://www.bbc.co.uk/news/uk-11521919