Strange.
In my experience as a German, everyone instantly switches to English if just one non-German speaker is in the group.
I suspect it's largely a generational/regional thing. My wife has lots of family from various rural parts of Eastern Germany, and half of the people over 50 speak effectively no English.
It’s definitely generational and regional. It’d be hard to find a young educated German in Berlin who doesn’t speak English well.
They probably learned Russian in school in the former communist part of Germany.
Do they know Russian? They had no reason to learn English if they’re over 50 and lived in East Germany, for obvious reasons. Someone that is 50 now would’ve graduated high school in 1993, only a few years after German reunification.