I think they meant you could theoretically "run a few shell scripts" to install and uninstall packages and configuration to change stock Ubuntu to Pop (or Elementary or whatever) since the core OS is the same.
The very first concepts of Pop were like this, but since then the OS has grown to be much more complicated than that. There are some fundamental system configuration changes that make that a very difficult (if not impossible) task right now. It would be like converting a Debian system into Ubuntu.
It's not _exactly_ a diff, but here's a link to the Pop!_OS github page, which contains 149 repos (only 16 of which are forks) https://github.com/pop-os
> one could take Ubuntu and run a few shell scripts (I am grossly oversimplifying) and boom you are now running Pop.
That same link notes that the top languages for the Pop!_OS repos are Rust, C, Python, JavaScript, and (lastly) Shell. So not _exactly_ "a few shell scripts". (I don't know how accurate that really is, but I do know they've written a fair bit of Rust.)
(Note: I don't currently use Pop!_OS and think the name is absurd)