I can't discuss exactly to how is applies in the context of Gay Berlin but I can certainly give an overview of how the post-war demobilization worked, or, in some cases, it didn't.

With the utter collapse of the German central government, there was really no longer any real authority to disarm and maintain control over the German military. This was especially true in the Eastern fronts, where units were essentially told that the war was over and to make their way back home. Some areas, like the German Eastern Command-"Ober Ost", which was the German occupation force in Poland and Lithuania, remained in place as part of an effort to both keep the Soviets out of the resulting power vacuum, and also in part because elements of their command remained intact-in this case, Max Hoffman was the direct commander and was able to maintain control over his troops until he withdrew them back to German territory in December 1918. Other units had less direct control and instead ended up just taking the nearest possible train back, often using force to "convince" the local authorities to allow them to do so. Some units were interned by the local authorities and disarmed, others made it back to their garrison towns still equipped. From there, troops would demuster and reorganize, with some soldiers returning to their homes (which, if a soldier from Alsace was part of a unit based in Saxony, could be a long train ride away) and other units involved in maintaining order.

There was a sort of revolutionary fever in the air. With the collapse of the imperial government, many towns started to create so-called "Workers and Soldiers Councils" which directly administered the towns. Despite being associated with the revolution, for the most part these councils were dissimilar to the local soviets formed in the wake of the Russian Revolution in that they were centered around the power groups in the local towns (the labor unions and the armed forces) rather than ideological leaders.

In areas of dispute, such as those territories disputed between Germany and Poland, a low-intensity conflict raged on between Polish and German irregulars. Many German troops, disastified with the new way of things, and especially suspicious of foreign attempts to grab what they considered German land, declared themselves Freikorps (free corps) and acted as irregular militias to fight against whatever they felt was a threat to their idea of Germany. Freikorps fought as far as the Baltics against the Bolsheviks (as well as Latvians and Lithuanians), in Prussia, Posen, and Silesia against the Poles, in the former Austrian-Hungarian Empire, and even in Germany against socialists and communists-both suspected and otherwise. The Spartakist uprising in January 1919 and another one in the Ruhr in the early 1920s were both crushed brutally by Freikorps units, who often acted solely on the command of their immediate officer. This especially became the case in the wake of the signing of the Treaty of Versailles, when many units which had otherwise been reintegrated into the regular army were disbanded to comply with the military restrictions of the treaty. These units, instead of returning to their homes, declared themselves Freikorps and acted accordingly. While the central government was able to exert a certain degree of control on these Freikorps (Gustav Noske, the defense minister, had managed to use them to crush several political threats to the administration) they also posed a threat to the government, so they were eventually disbanded. This was a valid concern for the government, as for instance during the Kapp Putsch where the regular military stood down while former Freikorps elements attempted to coup the Weimar government in 1920.

All in all, for your typical German soldier, the "demobilization" was essentially a massive trainwreck, where your best bet for survival was to stick to your military unit until you could get home. After getting home, there was a good chance you couldn't readjust to pre-war life, and in doing so end up joining an organization full of similar disaffected former soldiers, whether it be a militia or a political party. Most of the political parties often had a paramilitary component to them, and not just the obvious ones like the SA (the Nazi paramilitary force) or the Rotfront (the Red Front, the paramilitary of the German Communists, the KPD). The Reichsbanner Schwartz-Rot-Gold was the military arm of the Social Democrats (SPD) that were initially in power in the Weimar Republic, for example.

I hope this helps.