You are right they are just cleaning it up. Common sense goes a long way, do we really think they are loading it and going to mow down trader's row?I see no indication that it is being loaded. Looks like the guy on the business end has a rag for polishing.
The guy on the breech is holding it down so it doesn't move around. I do not see any balls or powder bags near the cannon.
HOPEFULLY that is the case, but from a mere picture, we are only guessing.