It may be coincidence, placebo effect, spontaneous remission, effect of other meds/supplements to name few...
I am sorry but this "buried research" was abandoned many years ago by peers. Yes, of course SCD worked for celiac disease because of gluten exclusion. It does not necessarily mean that it will work for IBD.
There are not only thousands of anecdotes out there about
dramatic improvements from SCD/IBD-AID/Keto/etc but also studies showing decreased inflammatory markers, endoscopic improvements, and ability to ween off medications (all of these are due to decreased inflammation) when following such approaches.
I agree food intolerance is part of the equation, but I don't see how you can think inflammation is not also part of it given we do have data on this.
Ultimately, the common thread I see in just about
all of these diets is a focus on whole unprocessed foods. I assume this is in part why we see higher rates of IBD in the westernized world.