How the Gallic War started

For ancient battles they usually tried to make the enemy numbers more impressive by including their entire population, including women and children/elderly. For most of those battles you can comfortably reduce the enemy numbers by like 2/3.

Even though he still was outnumbered basically every battle even with accurate numbers, he was sending professional legions against shit-smeared frenchmen so he usually had the upper hand in the field (although Rome did have famously awful cavalry compared to the Gauls or Germoids). A lot of generals could have won many of his specific battles but almost no one could have managed the entire campaign. His real genius was in things like maintaining his supply lines, knowing how to be in the right part of Gaul at the right time, playing the tribes against each other to keep them from uniting until it was too late. He was one of the best ever at stalling, retreating, doing whatever he could to prevent an engagement when he didn't have the upper hand, and knowing exactly when to pull the trigger when everything lined up in his favor.

Though some of the finer details are definitely false, there were so many soldiers and people with him and so many people who'd use that it was a fabrication as their advantage that by and large it's pretty accurate.