Imho the public_name field for executables is an unnecessary distraction for beginners and should be removed from getting started tutorials. It is not mentioned on the dune landing page which shows a tiny example: https://dune.build/
See also Draft tutorials on Modules, Functors and Libraries - #2 by yawaramin
Simplicity is super important when getting started. A 1-to-1 correspondence between the source file name and the target executable file name is the kind of simplicity that we should not easily pass up.