What do each of the columns mean? Some of them
are self explanatory, but I don't understand %Kurbel, Naufwinde, and
E? Does anyone know the equations behind the data? I'm guessing they
are related to thermalling, but I just can't figure them out.

You are right:
%Kurbel is the thermalling percentage
NAufwinde is the number of thermals
R/C is average climb ratio
E is the glide ratio

I think the formulars are quite clear, may be apart the %Kurbel, there
is some freestyle in the definition.