Is there a difference in the upward nod and the downward nod?

I was just noticing in Mtl_Zach’s question there were some people saying they just gave “nods” when acknowledging or greeting someone. I always thought the upward nod was more of a positive/personal “Whats up?” and the downward nod was just a non personal gesture maybe from back in the day when people tipped their hats.