What you have here is a merge conflict. You can read here for more information about how IntelliJ handles conflicts under Conflict Resolution Tool here: https://www.jetbrains.com/help/idea/2016.2/resolving-conflicts.html
The "strange text" is injected into the conflicted file by Git, so you would see these even outside the IntelliJ merge tool. If the local and remote content differs, a line of = signs will be the divider between your local version and the remote version. In this case since both revisions are equal, you simply have a single line conflict with the same content from both sources.
Essentially, you need to choose which revision of the code to use by selecting the chevrons & X's on either side of the window panel of your screenshot. There is also a handy 'merge non-conflicting changes' button that makes reviewing the actual conflicts much easier.