Which I found surprising in turn, because I assumed that this was the sort of information that people absorbed naturally? I mean, lots of what I know is from Jewish characters in tv shows and books, and some from documentaries, and some from reading about cooking all the time.

Well, you come out of fandom where people tend to pay attention to details and/or mostly try to research things (with varying degrees of success) and ask questions about details related to their characters.

There's always that "oh yeah" moment when you have that reminder that most people just passively consume media and don't think deeply about it, or ruminate over it at all.

Our diasporas make strange travelling companions of us all.

Yes, indeed they do.