I have passed the same thing you describe. They were rolled up tomato skins. I get them every time I have a salad or tomatoes in a sandwich within the previous 48 hours.
That is not to say they could be something else, but mine looked like short red sticks. And when unrolled, they were long and flat, about the width of the sliced tomato.
Same thing happens with potato skins, and chunks of garlic. I don't seem to digest them either.