There has been other evidence. In the body of the paper in the first paragraph the authors talk about a few other disease mechanism some of which have physical evidence associated with them. For example microscopic abnormalities have been seen in individuals with post-infectious IBS. Some of the authors of the paper published previous research on the role of mast cells which likely set the stage for the current research that was reported. Here is what the authors say "Currently, disease mechanisms involve components of the central nervous system, peripheral organ dysfunction and altered visceral sensitivity, prior enteric infections, microscopic abnormalities in the gut wall and/or signs of low-grade mucosal inflammation and immune imbalance and an impaired mucosal barrier function."
The findings report in the article you linked to is a particularly interesting physiological finding. It will be interesting to see how this line of investigation proceeds.
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