Hawkeye writes, "Kilroy," in the dust on the bus window as BJ is looking over the window with his hands and nose resting on the edge. This is a reference to the "Kilroy was here," phenomenon which began during World War II and continued through the Korean War. It was common for soldiers who were the first at a location to write the phrase, or the corresponding doodle of Kilroy as a cartoon face with a long nose hanging over a wall (as BJ is imitating,) and claim that Kilroy had already been there. It further became a challenge to be the first to write it, with soldiers even going so far as to write it in generals' latrines and other difficult to access locations.
This episode does not contain a laugh track.
Playing a North Korean soldier, Soon-Tek Oh surrenders as he also does in another "M*A*S*H"; "The Yalu Brick Road".
The weapon carried by the North Korean Soldier is a German MP 40. While this might seem like a goof, many weapons from the stocks of the German Wehrmacht - including the MP 40 - later wound up in the arsenals of developing countries supplied by any of the former Allies. Some have been known to be used in the Korean theater of war.
Colonel Potter reveals in this episode that during WWI, he got separated from his unit and wandered lost and hungry in France's Argonne Forest for three days before being taken prisoner by the German enemy, who shaved his head and "beat [him] to a pulp." This most likely occurred during the Meuse-Argonne Offensive, a major part of the final Allied Offensive of the war that stretched along the entire Western Front, lasting from September 26 to November 11, 1918, when the Armistice was signed. Therefore, it's logical to assume Potter was held as a POW by the Germans until the end of the war.