The American Revolution was not a civil war because a “civil war” is typically between two groups within the same country. For instance, Parliament and the King fought each other in the English Civil War. Similar conflicts occurred between the Union and the Confederacy during the American Civil War.
Contrarily, the American Revolution was a conflict between a colonizer and a colony. Usually, these are not referred to as "civil wars," but rather as "rebellions," "revolts," or (to their supporters) "wars of liberation."
Any of these might constitute a "revolution," so long as it alters society, the economy, and culture fundamentally as well as the leadership. As you can expect, this makes the word "revolution" very political. The proponents of change refer to it as a "revolution," whilst the opponents use a less admirable term.
The Civil War would have been referred to as a "revolution" if the Confederacy had prevailed, and the Union may have even done so at some point. Instead, it fell short, and now we refer to the conflict of 1861–1865 as a civil war. It's just another instance of how the winners write history.
