If the gallbladder is less than 2 cm (it is normally about 3 cm) after an 8 hour fast it is called a "contracted gallbladder". It is a sign that you have recently had Gallstones and you would also had other symptoms to support this, such as, abdominal pain, fever, jaundice, etc. This appears to true in your case. The walls and internal surface is checked for scarring and signs of disease and this appears to show no signs in your case. The scan will also show up signs of biliary sludge and detects sludge balls or tumcfactive biliary sludge resulting from biliary stasis. They show up as mobile masses that move as you change position. The ultra sound also checks for cholesterol polyps that result from accumulation of triglycerides and cholesterol in the gallbladder wall. Your gallbladder appears to be in good order except for its unusually small. It may grow larger when you return to a regular diet but it may just be a small gallbladder.
A smaller gallbladder may also be present in people with chronic constipation and studies show that that there is a link between slow intestinal transit and Gallstones due to bacterial toxicity in the gut.