What would give Swiss Chard a gritty texture? I made Swiss chard rolls last night and when we would bite into them there would be this gritty bite once in a while, almost like biting into a small gravel. Swiss chard itself has a gritty texture but this was definitely "stone-like". 

When I was washing the Swiss chard leaves, I did notice its texture to be grainy but not to the point of "dirty". Has anyone else encountered this? Do you think I just didn't wash the leaves thoroughly enough? I can't imagine it coming from any of the other ingredients from the recipe. Sure I had some stalk from the Swiss chard, chopped mint, and chopped arugula but it sounded like a stone.
The recipe you linked to has lentils in it. Most recipes with lentils tell you to rinse and drain them, and also to pick over them for stones. Lentils are seeds from a plant, and during their harvest, it's not uncommon for small stones to be picked up as well. (Same goes for rice and any type of legume.)

If you didn't check for any small stones before cooking your lentils, your encounter with "stone-like" objects is probably, in fact, due to stones.