In the words of Reading Rainbow host LeVar Burton "You don't have to take my word for it."

, but I can guarantee you that Mr. Marianski is referring to weight rather than volume.
I see your point about the book being titled with the word "Home", but you will notice that that does not keep Mr. Marianski from using the metric system coupled with US conversion for every single one of his recipes within this... "volume"

. There is no recipe of a meat product in that book that is scaled by volume measurements.
You could try an experiment. Try the recipe once by volume and then weigh out the ingredients. Then, try the recipe again sourcing the ingredients from different places and repeat the process of checking the weight of your volumes.
A faster way to see where these difference lie would be to measure 1 cup of Morton's kosher salt and then measure 1 cup of Diamond Crystal salt. The differences in weight are definitely worth noting.