If you can't get a look at his urine, just look for other signs of bladder issues like urine dribbling, urine stained fur, and straining when peeing. Not that the small poop is from a urine issue, just one common possibility can be from bladder pain. It could also just be he had an upset stomach for some reason, but if the small poops continue and are consistent, it means he isn't eating as much and that is causing the gut slowdown and small poops. This would be due to some sort of discomfort or pain from something. Trick is, figuring out what exactly.