Making this post because it seems lots of people don’t really understand what makes a Jew an Ashkenazi.
Ashkenazim are the Jews who moved into Europe during the Middle Ages, starting off in the Mediterranean and Eastern Europe and eventually making it all the way to England. Most Ashkies lived/live in Eastern Europe, especially Russia and Poland.
There are also smaller Jewish groups in Europe who are not Ashkenazi, such as Sephardi and Italkim.
Now, even though different Ashkenazim lived in different countries and had variations in their culture, they were/are still of the same ethnic group. A German Jew is an Ashkenazi who’s from Germany, and they are ethnically the same as a French Jew, a Romanian Jew, or an Estonian Jew.
Basically, a German Jew doesn’t mean someone who is half Jewish half German (although being mixed is certainly a thing) but a Jew who lived in Germany. Most Ashkenazim didn’t mix with non-Jews, so your average Russian Jew wouldn’t be part Russian.
One thing that could make this confusing are Ashkenazi names, such as ones ending in -stein, -burg, and -sky, which are actually European names. Jews traditionally didn’t have surnames, so Europeans forced them to choose a local one, that’s why there are Jews with German and Polish names.