Why was my bread mix really dry and take ages to knead properly?
FLours differ in their ability to bind water. The reason why our recipes work with the AP flour in the supermarket is that the mills adjust the flour int he supermarket to behave in roughly the same way - and by "adjust", I mean they really measure several parameters of different grains and blend it until it performs in the usual way. (They have to change the actual blend frequently, because even with the same wheat cultivar, growing condition differences due to location and weather mean that each batch will behave differently). 

I don't think there is some kind of deeper explanation here than just saying what you already observed - this flour is not formulated to behave like the typical AP flour, it produces a different amount/strength of gluten for the same amount of hydration. You might want to try baking the recipe from the package and see if you prefer it.