With the Conditions of Entry stating entries must be 'photographic, archivally sound, still and two dimensional', that seems to leave it somewhat open to interpretation I think. I agree though that photos and artwork need to be able to stand alone; a description may be in the catalog or accompany the artwork, but it isn't necessarily part of the display - and if it needs to be explained then I don't think the artwork expresses what was intended.
This must have been exposed to light at some point, being dark. I don't know the specific steps of the process but I think the grandmother would have made the marks on the piece of film while the film was out in the light. Even if it was indoors with enough UV/sunlight coming in the windows it would be getting exposed.
When I've done lumen prints using old photo paper I use a small table set up in a window and if it's a really sunny day I have to be careful to get the paper out of the black packaging at some distance or it will start to darken before I even get set up. (You gotta work quick or you get a big white thumb mark on the paper!). On more cloudy days I still am getting the UV light but the paper doesn't expose as quickly, and with the ISO of photo paper being in single digits obviously there's a longer exposure time than film.
Unless maybe this was a piece of film that had already been exposed to light, run thru some developer, let dry, then the grandmother drew on the already exposed, darkened film. I don't know if/how that would work, or if it would be considered to be a photographic process.
If the film had not been exposed, but then run thru some developer etc. in a darkroom, it would still be almost clear plastic with a light gray tone (probably from the developer) because it hadn't been exposed to light (if it went directly from the film holder or roll film cartridge to a developing tank). The reason I know this is from times I've changed film midroll, and I'm working fast and later realize uh-oh, is this a roll I already had in the camera or one I haven't shot yet?? So I get it developed because I don't want to lose any photos... so it ends up as some negative images on one end of a long strip of light grayish film. So if someone took
that and marked on it with pens it would almost look like ink marks on clear/gray tinted plastic.
I did find an art exhibit of portraits from last year that were described as 'abstract, symbolic, and conceptual', that included at least one photogram, a photogravure, and a photograph. I was thinking looking at them, do they tell me something about the artist? do they represent the subject? I think so. Are they strictly photographs? I don't think so, but they were made with a photography process.
This Is a Portrait If I Say So: Identity in American Art, 1912 to Today
This one reminds me of when I first tried doing a lumen print after someone told me about them. I just stuck some objects on a piece of old photo paper and sat it in the sun to see how well it worked. That was a practice run as far as I was concerned. So I think in this case the process could have been taken further to represent the subject in a way that told something about the grandmother.