They reference the Rutgeerts study I showed many times, if you divert the fecal stream, the intestine heals.
When you actually filter the stool down to a size that is smaller than the size of bacteria, you get healing too.
The fecal stream is full of bacteria of course, including E coli, the mucus barrier is not a static barrier, it moves, mucus is mobile. If it didn't move around, bacteria would easily break it down. If you have a moving fecal stream full of bacteria coming into contact with that mucus layer, you get inflammation. Especially when those species are invasive are start to enter tissue.