The answer is no. They are not in a book group, they don't know anybody in a book group (OK, untrue, a few people did, but the connections appear to be pretty distant - and one book group has disbanded).
On the other hand, after I signed up for a weekend gospel choir workshop I found out that just about everybody in Germany is in a choir, used to be in a choir, wants to be in a choir, or is about to be in a choir! The dinner I was very late to on Saturday night because of the workshop: everybody there when I got there said they'd been talking about how they envied me and how they missed their days in the choir. The people who aren't in book groups: turns out they're in choirs. The neighborhood newsletters dropped in our mailbox, the info sheets hubby's institute gave us at the beginning . . . full of choirs!
Now, if only I could a. really read music, and/or b. still sing soprano, and/or c. manage to remember alto parts (as opposed to the melody, which I apparently always sang when I was a soprano) so I could sing with the altos, I too could be part of this great German multitude of choirs. Stay tuned!