Why does so-called "hard" bread flour make "softer" noodles than so-called soft AP flour?

I switched the recipe from eggs, milk and AP flour to bread flour, soymilk and olive oil and got some very tender noodles...seems like there would be more gluten in bread flour and thus a more chewy noodle...they turned out good, but didn't seem to "fluff up" as much as the original recipe. What is the difference between semolina and bread flour if they are both "hard" flours?? ...Oh, and it WAS a lot harder to roll and cut the noodles with bread flour..