Well, I believe I have scienced out a reasoning. I'm just going on what I've learned in my three upper-level classes and a little research, but I believe it scratched because that's a fairly sharp surface and chromium is a prominent element used in stainless steel. It has an 8.5 hardness on the Mohs scale, which means it's closing in on the 9 rating of sapphire (a form of corundum). As I mentioned before glass is going to be no more than maybe 6.5.
Honestly it's a case of bad luck. I mean objects made of stuff that hard with edges sharpened to any degree aren't really found in most places. You'd pretty much find thing in scientific areas or workshops with nails, drills and other stuff like that. I really wish I knew how to help reduce or get rid of it, if there is a way. I just killed my iPhone screen so I know how that feels. But if you want a silver lining, it makes me feel better to know I got the Watch version since I'm sure stuff like that will be around me as I take these classes and find a job in the field. I have been clanking my watch on my seat belt buckle about every day, so I'm definitely glad I went for the stronger watch since I have obvious clumsiness issues.
If you have a teacher who is knowledgable about minerals and geology, you oughta run that hypothesis by him or her. I'm curious to know if I'm right. Maybe I should email the Mythbusters on that one.