The buildah docs for installation mention,
sudo dnf -y module disable container-tools
Interestingly, the advice for RHEL 8 BETA is to enable them
sudo yum module enable -y container-tools:1.0
What does this line do? And by extension what is container-tools and why do I want to disable them?
Modules are a new way of package management, it is basically a set of packages shipped together and it allows to provide different versions of software. If you are familiar with CentOS 7 Software Collections, modules are replacement for them (but work in a different way), see man dnf.modularity for more details.
The container-tools module provides container tools -- buildah, podman etc. you can get detailed information about the module using dnf module info container-tools. There are multiple versions of the container-tools module with different versions of the tools -- container-tools:rhel8 with latest stable version, container-tools:1.0 with version from 8.0 and container-tools:2.0 from 8.2, see this article from customer portal.
By disabling the module you are basically saying "I want to ignore this module and never install it". The documentation mentions it in the section describing installation from a third party repository with latest versions of the software so you need to disable the module to avoid conflicts to be sure the latest version will be installed and not the version from the module.
