I come across this a lot, and a lot of people have different approaches.
Personally if the Bandcamp page has a catalogue number in it, I put in a label and CAT no.
If it doesn't I don't.
If there's two pages (eg a label page and a band page), I will add one as the 'label' release and one as '[no label]'. You can click on 'feed for this album' at the bottom of the BC page to find the 'real' digital release dates for that version!
As jesus2099 says though, in this case the cat no looks like it's describing the 7 inch.
So for this I would look at their other digital releases, if most don't have a cat no. then I'm guessing this one doesn't either. If they tend to, I would assume the 7 inch cat no also applies to the digital version.