https://gut.bmj.com/content/72/1/180

The study. It basically says that this is something one perhaps should consider in clinical settings and that the speed of fecal matter might be a worthwhile direction for future inquiry.

"Altogether, a better understanding of the complex, bidirectional interactions between the gut microbiota and transit time is required to better understand gut microbiome variations in health and disease."

It does not say 'this is a sign of health and that is not'.