This is because both the Union and the Confederacy were using their own maps, which did not always agree on the names of places. This is an example of the difficulty of communication and coordination during the American Civil War.
In addition, some battles were given different names by the Union and the Confederacy because of the different perspectives they had on the war. For example, the Battle of Bull Run was called the First Battle of Manassas by the Confederacy because it was fought near Manassas, Virginia. However, the Union called it the First Battle of Bull Run because the battlefield was near a creek called Bull Run.