You could ask your vet if you could bring in a ziploc bag of his droppings to check for parasites. Flubenvet or Flubendazole are good for worming. Harkers Coxoid is used for treatment of possible coccidiosis. Those are easy to get without a prescription. It sounds like he is having no symptoms...
That could be cecal poop. Are all of his poops like that? Here is some reading about cecal droppings:
https://the-chicken-chick.com/whats-scoop-on-chicken-poop-digestive/