I think that explanation for elevated values is valid as many livestock feed products are the byproduct of the food industry.
However, the feedstuff you offer your chickens is going to start out with the identical values you give other livestock. If you toss your chickens one pound of corn, it will have 1.6 Mcals. 36g of protein, X of minerals, X of vitamins, X of fiber... If you feed another pound to your heifer, it will have 1.6 Mcals, 36g of protein, X of minerals, X of vitamins, X of fiber. Nothing changed I can take the analysis values out of an equine nutrition textbook and use them in any situation. The raw data will not change. Most all this information was gathered by the cattle industry. My book credits the dairy industry for the charts. They have the deep pockets to do the research and it will have a greater impact on their profit margin. There is almost zero groundbreaking research done in poultry nutrition because they can use the initial information the cattle industry has spent millions on researching and use it at no cost. I can not extrapolate how a horse digests and uses a feed product and expect any other animal to digest and utilize it the same way but the building blocks at the start of the process are the same.
If I were to eat this same sunflower seed product, I would still have 30% protein available to me. How I use it is up to me as a human plus my individuality. The analysis is not going to change just because I ate it.