As john buford tracks the confederate army, he stops to wave at a rebel officer. why would he greet an enemy in this way?

There could be two possibilities for this action:
The first possibility is that he was simply arrogant
The second possibility is that he was a true soldier and a fighter. He wanted to show the enemy that he was not afraid of him and that he was ready to face him and fight him (if the situation required a fight)