If you can rule out what you are eating as a cause for the green stool, then you can assume it is just bile. Basically, green stool occurs when there is very rapid transit and the bile has not had time to change color.
Bile starts out green, changes to yellow, orange, then brown.
The green color is NOT a sign of infection, but just transit time. Very rapid transit could be due to infection (like food poisoning or gastroenteritis), obstruction (yes, I know, it seems counter intuitive, but the gut works harder and faster if there is an obstruction), or food intolerance or general upset. Could even be a troublesome gallbladder. Sometimes it resolves before we figure out the cause.