The Soviet officer is Semyon Krivoshein, he’s Jewish and not celebrating for multiple reasons. The Nazis occupied Brest when they weren’t supposed to, Krivoshein got there and started negotiating to try to get them to leave. The Nazis were making a propaganda film out of this (which is where the picture comes from) so they wanted the Soviet army to have a parade with them. After an argument Krivoshein agreed that just him and some of his staff would stand there and watch the Nazis parade out of town in exchange for the Nazis leaving Polish prisoners they took in Brest.
Brest was 50% Jewish at this point, in Operation Barbarossa the Soviets defended for 6 days, Jewish Soviet officers were summarily shot by the Nazis, almost the entire Jewish population of Brest died in the Holocaust.
It really wasn’t a good time to be Jewish then. The muslim world wanted you dead, the nazis wanted you dead, the Soviets hated you, and the US and UK greatly disliked you. There was no place where Jews were actually safe and protected until after WWII.
Krivoshein was born into the well-to-do family of a Jewish artisan shop owner and in 1917 graduated from a gymnasium, a Russian secondary school for the educated elite. In 1918 he enlisted in the Red Army to fight against the Whites in the Russian Civil War, seeing service in the 1st Cavalry Army of Semyon Budyonny.
Krivoshein continued to command his corps until 1946 when he was appointed Head of Department at the M. V. Frunze Military Academy. In 1950 he moved to Odessa to command the mechanized and tank forces of the small Odessa Military District. In 1951 the Ministry of Defense selected him as a candidate for the Soviet Army higher command and sent him to study in the Higher Military Academy of the General Staff. Krivoshein graduated in 1952. The death of Stalin in March 1953 brought an end to Krivoshein’s military career: as the new leadership began to reduce the huge Soviet army and, on May 4, 1953 the Soviet Ministry of Defense retired him after 35 years of service. He spent the last quarter century of his life writing four books of his war memoirs.
Unfortunately, this man was an exception, not the rule.
http://en.m.wikipedia.org/wiki/Antisemitism_in_the_Soviet_Union