Earlier quoted context omitted.
I'm on my phone so I'm too lazy to dig for this, but I'm pretty sure they're talking about the bit of shell script that gets run if you type a command that isn't found in PATH. Fedora and Debian will both dive straight into searching apt/dnf for a matching package and ask "do you want to install this?" I imagine you could create a hook that gets run for any command failure, but again I'm on my phone so not sure.
It's https://packages.debian.org/sid/command-not-found
In /etc/bash.bashrc:
# if the command-not-found package is installed, use it if [ -x /usr/lib/command-not-found -o -x /usr/share/command-not-found/command-not-found ]; then ... fi