Good catch. Sure enough, I had that file set and didn’t realize that it was the source of that functionality and not built-in to psql.
Here are the contents of my ~/.editrc file:
bind "^R" em-inc-search-prev
This is part of my dotfiles: https://github.com/andyatkinson/dotfiles
With this file present, then reverse search works within psql as described. I’ll add something about this to the Rideshare repository for others. Thanks for reporting it!