No, there’s a clear link between gut microbiome and behavioral/mental issues that has nothing to do with physical digestive symptoms. It’s been seen with other disorders, like depression: https://hms.harvard.edu/news/drawing-line-gut-microbiome-inf...

It's a bit speculative. They need placebo-controlled trials and so far the results have not been very convincing for many psychiatric outcomes. There is exciting research around gut microbiota, but many of these studies which make rounds in HN and other online forums, seem to be mostly open-label or uncontrolled studies.