I believe the authors are riffing off the wonderful 1970 Counterexamples in Topology[0] book. There's a minor tradition of this among the cognoscenti. The topology book is an absolute gem and very approachable if you have working familiarity with the fundamentals.

[0]:https://en.wikipedia.org/wiki/Counterexamples_in_Topology

Counterexamples in Type Systems: programs that crash, segfault or explode (2021) - https://news.ycombinator.com/item?id=36213704 - June 2023 (97 comments)

Counterexamples in Type Systems - https://news.ycombinator.com/item?id=27252899 - May 2021 (62 comments)

Appropriate.