I am sorry to hear about Rudder's diaper escapade. I can see why he would have quite a tummy ache at the very least.
Just to be clear, he is not vomiting, right? And he is still eating?
If so, then I would be less concerned about an abstraction at this point, although one may develop depending on how much diaper material he ate.
As long as he is continuing to eat and is not vomiting or straining to defecate, you can continue to watch him at home however, if he is vomiting has a painful abdomen, stops eating or is straining to defecate, I recommend having him seen by a veterinarian for diagnostics to rule out intestinal obstruction.
If you want to err on the side of caution and be proactive instead of reactive, you can take him in (tomorrow to your regular vet or into emergency tonight- your preference) and have radiographs or abdominal ultrasound performed to look for evidence of foreign material or obstruction. If there is evidence then you will have to discuss with the veterinarian the pros and cons of surgery vs in hospital treatment with IV fluids and supportive care to see if he will pass it.
What was he doing when he yelped? did he seem to have abdominal pain? if so, I would lean toward taking him in sooner rather than later but if it wasn't localized you can continue to watch him.
Does this help to address your concerns tonight?