See my other response, it’s very much not random. Every processed product in the modern world is hyper optimized for profit. At the least , they know the average weight of shell with nut and without in grams or something smaller. Also likely a hopper with high speed cameras to count yield per bag to maintain exact profit margins. There could be, and likely is, a scale at the end of line that weighs and would five a fairly faithful estimate of empty percentage per bag. And all that is automated.

Problem is that infrastructure likely exists more or less and they have just turned up the acceptable percentage of empties probably. Like anything else, VC pushes those lines quarter after quarter until people might revolt (or in another time, an administration regulates an acceptable amount of “defective” product).