Basically if you change the data in an exported or purchased module, the playing campaign you changed it in - keeps those changes.

Updates to the changed exported module doesn't effect the changes since it is assumed you made the changes for a reason. The revert changes at the module level lets you use the module as it was exported and throws out any changes. You can also revert changes at the individual record level, ie maps, images, npcs etc.

Since you re-exported everything it was fine to revert the whole module back to the baseline export, but you may not always want to revert the whole module.