It's very difficult to see what it can possibly be. Was the foreign presence moving? Because from the image, it almost looks like a fuzzy fungus. If the poop was wormy, definitely a parasite issue and means vet intervention is necessary. If they're little white bugs, then I imagine it's what Herpin Man is describing and you happened upon some springtails.

I would also recommend letting your substrate dry out just a little. It looks saturated with water which can create problems.