You don't understand perspective. From the tv camera the pitch is shaped like a trapezoid, not a rectangle, so every offside line will be an increasingly incremental angle the further you get away from the half way line. That means that the two comparable lines used for the last defender and the attacker will not be parallel.
But I agree, it's barely offside enough to be called offside, it's half a boot offside, so should be given the benefit of the doubt, especially at the speed the move was. Still, seeing as every decision seems to get analysed it's to show how it works both ways.