This took place a good 10+ years before the book, so maybe word got around. ;o]
Maybe it was a folk custom that the author heard of.
Last year when I was at Mom’s at the beginning of Lent, we were at dinner with five or six of her friends, and Murray, who is 102, said, “I’m giving up sex! What about you?” All the old ladies were widows and said, “What a good idea!”