I Just Bit Into A Rock

I need advice! My boyfriend bit into a rock at a local fast food restaurant. (We ordered on door dash) He was eating the chili cheese fries when all of a sudden he bit down on something hard and stopped chewing immediately. He spit out what was in his mouth and looked to see what it was. It was a ROCK!!! It chipped his tooth!!! We called the restaurant and spoke with the manager who said he has been in business over 20 years and he has never seen something like this. He asked us to bring in the food and rock. We did. While there, he took the food and rock, refunded us via cash, and said he would report it to door dash. He defended their restaurant and explained how the meat for the chili goes through a grinder that grinds the meat so it's not possible for this to happen. My boyfriend questioned the manager saying: Isn't the food bagged on camera and tied shut. The manager replied yes. We did express our concern about his chipped tooth but he seemed to shrug it off. We eat at this place often. Last time we ordered, our food was wrong. We did report it to door dash who refunded us about $7. I am not sure if this is retaliation in a way or if I am overthinking. We are not sure what the next step to take is. Any advice would be great. He had near Perfect teeth and now his tooth is chipped!!!