When it comes to numbers on the battlefield every sane historian of our time agrees they are inflated. It was not just Caesar it was common practise, which is also one of the reasons Caesar could get away with it. Ancient historians and writers also refer to the practice. The argument of the soldier being able to refute the numbers isn't very good either, first we all know the soldiers were rather loyal to him, furthermore few of them would have the possibility to speak up anyway as that was a very limited privilege. Then remains the question of when it was publicized. If it was after the civil wars, well you'd be a fool to speak up either way. Unless you wanted to end up on the capitol. Also due to the nature of the irregular peasants army and strategic situation I even bet Caesar wouldn't even have a clue about the numbers the army had.

Just applying modern day logic and possibilities, situations, reactions,... on the ancient period really doesn't work. Not at all actually.