IIRC, someone mentioned to me once that bash doesn't link against libreadline, but uses libreadline (the source is directly in the Bash repo), so it's possible

IIRC, someone mentioned to me once that bash doesn't link against libreadline, but uses libreadline (the source is directly in the Bash repo), so it's possible that it's using GNU readline, while Apple's libreadline is a BSD flavour.