Prepare the grill for direct and indirect cooking over medium heat (350° to 450°F).
In a small bowl combine the rub ingredients. Lightly brush the ribs on both sides with oil and season evenly with the rub. Cover and refrigerate for 1 to 2 hours. Allow the ribs to stand at room temperature for 15 to 30 minutes before grilling.
Brush the cooking grates clean. Grill the potatoes over indirect medium heat, with the lid closed, until tender when pierced with the tip of a knife, about 45 minutes, turning once or twice. Remove from the grill and let cool. Meanwhile, make the chowchow.
In a medium saucepan over medium high heat, warm the oil. Add the mustard seeds and cook until they begin to pop, about 1 minute (if the mustard seeds don’t pop, the seeds will be too crunchy and won’t have much flavor). Have the lid handy to keep the seeds from popping out of the pan. Quickly add the onion, bell pepper, and jalapeño. Cook until the onion is softened but not browned, 3 to 5 minutes, stirring often. Put all the remaining chowchow ingredients into the saucepan and bring to a boil. Reduce the heat to a gentle simmer and cook, partially covered, until the liquid reduces and the vegetables are softened, 8 to 10 minutes, stirring occasionally. Remove from the heat and let cool.
Cut the sweet potatoes crosswise into 1-inch slices. Brush the slices on both sides with oil and season evenly with salt and pepper. Grill the ribs over direct medium heat, with the lid closed, until cooked to medium doneness (145°F), 15 to 20 minutes, turning four times to brown each side. Remove from the grill and let the meat rest for 5 minutes. Meanwhile, grill the sweet potatoes over direct medium heat, with the lid closed, until they are lightly browned, about 5 minutes, turning once. Serve the ribs warm with sweet potatoes and chowchow.