Is there a chance that it could have been gas? Some snakes do fart before passing feces or urates. Also, make sure to double check your temps, if they're on the cooler side, it can affect digestion sometimes.
If he's due to shed, I would skip this meal and feed him after he sheds. Was he in blue? or is it just an estimate since last time he shed? Sometimes shedding can also affect the digestion process for these guys as well.
I would keep an eye on him regardless. If he makes and other wheezing sounds, gets lethargic or starts bubbling, obviously get him to a vet. But also keep an eye out for his next stool. If it still looks questionable, you can ziplock baggie it and get it tested for parasites.