No, yeah you do, you just said it in the previous paragraph: "And since iOS (and in some places now macOS, too) doesn’t offer visual affordances like scroll indicators, she had no idea there was any content further below."
I don't feel bad being critical of their UI choices, precisely because Apple was the company that made a big deal about UI and how far ahead of the poor hopeless gray conforming IBM Microsoft masses they were. And I mean, yeah I would've bought it, back then. Their stuff at its best was always a holy union of simple, functional and beautiful. But function came first, then simple, and beautiful arose from that, kind of in the Zen sense. Kind of like how a well-crafted hammer can be beautiful even though it's just a hammer. But at some point they went whole-hog into putting "beautiful" first, probably because that's where the money is. If you're not careful with that, you wind up being beautiful and stupid like the popular kids in high school. A beautiful hammer with no handle is just a crappy piece of shit. Even though it might be a great hammer(head), it's crippled by its lack of a proper UI.