The term Russian-German is a translation of the German Russlanddeutsche and Russian rossiskie nemtsy. In both these cases the word Russian refers to the territory of Russia or historically the Russian Empire which would include Ukraine, parts of Poland, Bessarabia and other areas outside the Russian Federation. It does not refer to Russians as a nationality. This is clear in the original German and Russian versions. In German you have Russland vs. Russe and in Russian you have rossiiskie vs. russkie. A more acurate, but really awful sounding English translation would be Russia-Germans. The translation Russian-Germans is standard in most literature outside the US and corresponds to the designation of other immigrant groups in the former USSR such as Russian-Koreans, Russian-Greeks and Russian-Finns.
In the US you often see the term German-Russians. If this is translated back into either German Deutschlandrusse or Russian germanskie russkie it describes an ethnic Russian living in Germany. Although many native born Germans view the Spaetaussiedler arriving from Kazakhstan, Siberia and Central Asia as Russians rather than Germans this is not why the term is used in the US. Rather it is a poor attempt to impose an American system of ethnic classifications upon Eurasia. I wrote earlier of Americacentrism distorting American views of other places and this is a prime example. The term German-Russian is meant to correspond with the term German-American. But, it does not. The American in German-American does not refer to the territory of America. Rather historically a German-American was a person in the process of assimilating from being completely German to being totally American. It was a temporary hybrid ethnicity of the second generation. In the 1960s and 1970s a number of activists in various white ethnic communities sought to freeze this assimilation process in order to use the ethnic symbolism of their ancestral origins as a tool for political mobilization. Hence the permanent existence of such catagories as Jewish-American, Irish-American and Cuban-American. Almost nobody in the US calls themselves a German-American. People of German heritage in the US are nearly totally assimilated and identify themselves as merely Americans.
The situation of people of German descent in the US is radically different from that in the former USSR. Since 1938 the catagory German has been an inherited and immutable legal catagory. It has been stamped on all passports, identification documents and other records of people biologically descended of German speaking immigrants to the Russian Empire in the 18th and 19th centuries. Regardless of how much they acculturated or adapted to Russian culture they legally remained Germans, a status they inherited at birth from their parents. Only in the case of the children of mixed nationalities did an individual have an opportunity to partially escape from this racialized legal catagorization. In the case of mixed parentage, a child had to choose the nationality of one of his parents when he turned 16. Otherwise nationality in the USSR was in effect a racial catagory determined by biological descent and not subject to change. This legal catagorization and the discrimination that went along with it created a pyschological identification of being German among Russian-Germans that were totally acculturated and would have otherwise become assimilated into the Russian nationality. Voluntary assimilation in the USSR and most Post-Soviet states was never an option like it was in the US. Legally a Russian-German was always completely German in his essence no matter how well acculturated.