The authors choice of words is terrible ("real work"), I'd phrase it as "making digital products". E.g., in the fitness instructor example, the product is of course the fitness training. I think most people who use this phrase "real work" are in the digital product business themselves, e.g., programmers, designers, even people writing for websites (although I think an iPad works decently well for web writing already, if you're willing to make a couple of adjustments). I think the author is only really looking at work through their own prism of being involved in making digital products. And files have been remarkably resilient in that domain (while there have been some inroads to non-file-centric workflows, e.g., No Code comes to mind). It's overwhelmingly how those products are made today, and, as the author points out, one of the iPad's biggest flaws, if you're trying to do use to make digital products, is it's resistance to working with files.

I agree 100% that calling it "real work" is terrible, but I still think the authors points about resilience of files in the process of making digital products are important.