Oh, I see. Those little bits may be all that can squeeze past an impaction. The same thing happens to human babies - they seem to have the runs, but actually it's what is squeezing past an impacted stool in his colon. For your ig, wait a bit longer. He could move the rest of his stool any day now. But like I said, if it goes on for another week and a half, IMO he then needs to immediately see a herp vet. It's very much in our and his best interest to not let him get deathly ill, that creates huge costs, and a lot of pain. The main trouble with owning iguanas is they are expensive to keep alive.
PS. I once had an ig who started straining and pooping as soon as he even saw the tub, what a hassle LOL.