In context, it actually was. It sparked off a decades long internal struggle followed by some 6-10 years of war in Continental Europe.
The internal struggle was largely bloodless. Sure, there were small scale conflicts between militias and aristocratic fixtures, but to say that it was a civil war is a stretch. Day to day life was not shattered as it was in the Former Yugoslavia, or Syria right now. If anything, it was civil war lite. The wars of the French Revolutions were successive invasions by foreign powers bent on reinstalling the French aristocracy, because they realized that if the French Republic stood it would foster similar anti-aristocratic movements in their own lands (the if-they-can-do-it-we-can-do-it syndrome). I wouldn't call that a civil war either.
Furthermore, the aftermath of the French revolution led to the eventual demise of European aristocracy, which would make this so-called civil war the best civil war that happened in history; hardly the most horrible.
To call the French Revolution the most horrible civil war is such an extreme exaggeration, especially if one considers that in Rwanda up to 1,000,000 civilians were slaughtered in a matter of just over 3 months. But I suppose those dark skinned folks don't matter as much as the enlightened French of the late 18th century did.
