repository tag under distributionManagement vs repositories?

You have it exactly right!

From the POM reference:

Where as the repositories element specifies in the POM the location and manner in which Maven may download remote artifacts for use by the current project, distributionManagement specifies where (and how) this project will get to a remote repository when it is deployed. The repository elements will be used for snapshot distribution if the snapshotRepository is not defined.

• Repositories declared under the distributionManagement element will be used for deployment, i.e. when running mvn deploy.
• The repositories element will be used for downloading dependencies of the project. The command is not necessarily mvn install but any command that requires Maven to fetch artifacts from a repository.