As others have mentioned, I do agree that it is appropriate for the restaurant to comp the meal(s) for the affected patron(s) only. And anything else is just an overall goodwill gesture for everybody in the party to continue eating there.
I told this story in a previous thread long ago, but I was having dinner with relatives in the McCormick & Schmick's (a chain of upscale seafood restaurants) in downtown LA a few years ago. Coincidentally, I also had a dish with mashed potatoes, and instead of a shard of glass in mine, I found a pea-sized pebble. Luckily for me, I either chewed slowly so that no damage to my teeth were done or located the pebble with my tongue. Otherwise, I am positive some damage would have resulted.
Fortunately, my meal was comped and we got free desert as well.