It's likely that a sinker is indicative of healthy stool. The actual article notes that floating stool is correlated to increased presence of B. ovatus which is

It's likely that a sinker is indicative of healthy stool. The actual article notes that floating stool is correlated to increased presence of B. ovatus which is "an anaerobic commensal bacteria linked with flatulence and intestinal bowel diseases" [1]. [1] https://www.nature.com/articles/s41598-022-22626-x https://www.nature.com/articles/s41598-022-22626-x