The same thing happened to me. I have owned every iPhone since 2006. I've never needed a screen protector. I've always been fully confident that the glass would not scratch. It's just a fact of apple's build quality. Yet, low and behold, I've treated the iPhone 7 plus the same as previous iPhone iterations, and my screen had a scratch on it. So I knew Apple (being the types to not admit a manufacturing defect), I would have to pay to have it replaced. So began my long wait at the Apple Store to get them to replace my screen. I'm told I have to pay $150. I wait 3 hours, and when they show me my iPhone with the replacement glass, the repair techs have scratched up the back of the iPhone. So, long story short, I got a next-to-new iPhone from Apple and this was only due to their calibration machine being down during the ordeal. When I got home, I put a screen protector on the iPhone. Since then, I've removed it, because it looks like crap. All I can say, from my research is the blame is on Gorilla glass 5. Apple assumed that Gorilla was producing a great product. Not true this time around. This whole experience makes me really hesitate to buy the latest and greatest.
Shame on Apple for not testing the products well enough, and shame on Gorilla glass company for pushing a shoddy product in order to milk customers of their hard earned cash.