There are several elements to this but the first thing is that the the question whether any Jewish people were directly involved is thinking way too conrete. Even if there were individual Jewish negotiators involved, the antisemitic myth behind the sentiment sprang forth from the idea that Jews controlled leftism as a weapon against the nation, often referred to by its adherents as "Judeo-Bolshevism".

The idea of a close proximity of Jew and left-wing ideology predates the specific myth of Judeo-Bolshevism and has a certain historical basis. During the formation of nation states in Europe in the 19th century, the question if Jews can be German, French, Russian etc. arose in the minds of a lot of nationalists and debates were had about the question of Jews as part of the nation. Seeing that liberal and left-wing parties were generally the political forces that advocated Jewish emancipation, a lot of Jews joined these parties, especially the non-religious bourgeois assimilated Jews.

Another basis for this myth was the nationalists' aversion against anything that was perceived as "international". Jews were seen as an interconnected international force whose individual members put their allegiance to "international Jewry" before their allegiance to the nation. In the second half of the 19th century, ultra-nationalist right-wingers in Germany and Austria for example ran campaigns against social democrats, Jews, and Catholics; for them the trifecta of internationalist forces.

With the Russian revolution, a lot of this was projected onto the Bolshevik revolution as the epitome of internationalist threat to the established system of nations and Capitalism. Seeing as how the Bolsheviks rejected traditional nationalist ideology, the idea arose that they were something akin to a foreign occupational force in many formerly Tsarist territories. Given how popular the myth of Jewish conspiracy was in Tsarist Russia (see the Protocolls of the Elders of Zion), the idea that Bolshevism was part of a Jewish conspiracy against the nation, took hold.

The myth really took off however, with the other attempts at post-war revolution outside of Russia. Recent scholarship has also pointed to the so-far little discussed German occupation of Ukraine and the Baltics in the closing phase of WWI and the associated military action they and Habsburg troops took against the Bolsheviks in the course of the Russian Civil War. Historians such as Joachim Schröder have specifically pointed to returning German soldiers and bureaucrats as a force for the spread of this myth. Another important source for further dissemination were the Freikorps, para-military units of former German soldiers fighting in the Baltics against the Soviets.

But in Munich especially there was one, the believe that Germany lost the war because the social democrats, socialists and the lefts that was organized in the Socialist Party and the USPD was responsible for the end of the war because they "knived" Germany in the back by getting the sailors of Kiel to strike instead of engage in a suicidal attempt to break the British blockade. And two, there was the Munich Soviet Republic. Following the sailor strikes, there wa spolitical upheavel in Germany. The vaccuum left by traditional power structures was filled by new ones, including revolutionary ones. In Munich a Revolution occured and communists and socialists seized power and tried to establish a new revolutionary left-wing order. This came hand in hand with violent conflicts with people who opposed communism and the left. And those opponents would also later come together with proponetns of the old order and the new German government and institute a violent supression of the left-wing order in Munich.

This experience of revolution and violence left a deep trauma on the city of Munich and the German psyche as such in the beginning of the 1920s. The right purported that it was Jews behind the revolutionary regime even using one of the involved people's Jewishness as "proof". This is the experience that Hitler was immersed in and bought into the anti-revolutionary rhetoric and deeds.

Sources:

• Gerrits, André (2009). The Myth of Jewish Communism: A Historical Interpretation.

• Kellogg, Michael (2008). The Russian Roots of Nazism. White Émigrés and the Making of National Socialism, 1917–1945.

• Levin, Nora (1988). The Jews in the Soviet Union Since 1917.

• Lorna Weddington: Hitler's Crusade.