The caecum is part of the gut, where all the bacteria are that produce the nutrients found in the re-eatable poo, I'm pretty sure (covered this briefly!) so that's probably where caecal comes from.
Sounds like these green poos are his caecal pellets then, they are getting more pellety now. Still don't see any in his cage (though I have noticed some "normal" poos), but each time I handle him, after a few minutes he does some green poos, some squishy and some better formed, and doesn't show any interest in them whilst I'm handling him.
Learn something new every day
