Hi steeleopads, the maths is simple, so I agree with your adding up.
Gross weight = 1012 kg
IGS says that WG imported 1000kg of seed [net weight]
Therefore 1012kg gross, less 1000kg of seed = 12kg for the packaging boxes etc. [it would need much more protection than plastic bags.]
The point is that 12kg to package a shipment with a net weight of 1000kg [seed] is not very much.