Oh Nicole, how sad.
That amount of crust shouldn't have affected him. I would give that to a dog.
If he isn't better in a day or 2, I'd really consider blood work. They don't have to show pain for it to be the pancreas and if that's the case food would be withheld. If he has been IBD free all this time and it was mostly mucousy poop before, I just don't know. Maybe the crust did have some grease on it. Although that dog in your yard sounds suspicious.
Did they do a fecal?