I could see rubbing past a jeans rivet doing that. (I mean, if the screen doesn’t scratch until Mohs level 6, maybe it shouldn’t do that, but I would always have expected that result. I don’t know how hard jeans rivets are.)
As for the speculation about who supplies what that the forum admins took issue with, it’s irrelevant who supplies the displays anyway, because the cover glass is separate. There is plenty of public disclosure that Corning supplies the cover glass (a formulation unique to Apple,* so not necessarily the same as GG 6, as people keep mentioning), so who makes the OLED underneath is irrelevant.
To tell you the truth, after I got a tiny little blemish on my iPhone X screen from (I assume) rubbing against something in a pocket, I became much more obsessed with how I carry my phone around. I don’t like screen protectors, and during the week when I’m in business attire in my office, I don’t usually use a case either. What I do instead is make sure that the phone never rests on or brushes up against anything other than clean cotton. I keep a clean white cotton handkerchief in my pocket that the screen goes against, and if I’m going to put it in a bag or something, then it goes into a case against a hanky or a screen-cleaning cloth, or into one of those hotel shoe-shine clothes turned inside out (so the softest stuff is against the phone). When I’m at my desk it sits on a cotton hanky. My family thinks I’m a bit nuts, but I like to keep this gorgeous thing new-looking and I’ve kept my XS perfect this way for nearly a year.
*Sources: https://www.cnet.com/news/iphone-11-has-a-few-more-features-than-we-first-thought-u1/, https://www.cnet.com/news/apple-invests-250-million-in-corning-for-future-iphone-glass-research/