Earlier quoted context omitted.
I think you have it backwards - he's saying that all German extension cords have a third pin for ground.
Oh yeah..I got it wrong. So, US doesn't have the concept of grounding? Surprising, but I suppose that does explain the sparks.
The sparks are caused by the physical design of the plug and outlet, specifically that US outlets are designed in such a way that you can actually see them. Any mechanical connection between two conductors (outlets, switches, etc.) has the potential to spark if the voltage between them is high enough. Other conductors have nothing to do with this potential.