I think it was meant as a joke. You could look at the end of the general moderation topic to see how it started.
So I take a particularly dim view of people who dismiss those who choose differently than them as virtue signalling.
In thus case it goes a little further. Jewish groups (for example) were calling her out on her stereotyping at the time, especially after the war. I’m pretty sure this qualifies as nervous self-interest, not virtue-signalling.
Here’s what a relatvely recent New Yorker article had to say:
Racism, anti-Semitism, and xenophobia turn up constantly in Christie’s books. In one, a hostess serves a special dessert called Nigger in His Shirt (chocolate pudding covered with whipped cream). We also get dagos, wogs, and Eye-ties. Most frequently commented on, however, are the Jews. In an early novel, “The Secret of Chimneys” (1925), Herman Isaacstein, who is, of course, a financier with a big nose, is invited to a political meeting at a country estate. When the host, Lord Caterham, is told who Isaacstein is, he says, “Curious names these people have.” Caterham starts calling him Nosystein. The others take this up and shorten it to Nosy.
