I think so - and the fact that it's so in the background speaks to how well the user experience is designed for iCloud. Apple pretty much surreptitiously hides the backup of contacts, photos, calendars, email (yes - a lot of people use iCloud mail), and lastly documents. The fact that Apple was so late to the game on iCloud Drive was that a lot of the shit that the average person doesn't want to manually back-up and monitor are handled in the background by Apple ("magically" to use their term.) I personally love Dropbox, but I would find it a nuisance to manage my contacts, or anything else beyond my documents and occasional photos backup.
Therefore, regardless of manual input necessary, it should still count as usage. I imagine a lot of people store backups on Dropbox, and that looks like it's counted in the article.
Yet, I am kind of surprised that the prevalence of Android software doesn't correlate to Google Drive market share.