I have this crazy idea. We could label the milk we buy at the supermarket as “zero cows”. This would mean that no cows are required when you buy, carry, store, or consume that milk. But if you buy your milk at a farm, then, well, this needs cows.
It seems silly, doesn’t it? And yet this is exactly what “zero emissions” means: “no emissions from the on-board source of power”. But there are emissions in the external source of power, right? Just as there are cows which produced the milk which eventually arrived at the supermarket.