Why does cookiecutter-django ask which version of Postgresql is installed on your machine? What does it do with this information? Update the docs? Set some settings? It appears to do nothing with this variable.
cookiecutter-django uses the information to create the postgres database in a container from the corresponding docker image at docker hub. It doesn't have any other impact on the generated boilerplate. Since you are not using docker this option has no impact on your described setup.
If you are still curious where this variable is being used take a look here.