Hull-less describes pumpkin seeds whose seed coat is not lignified.
That is the key trait of the Styrian oil pumpkin (Cucurbita pepo var. styriaca). A natural mutation, first noted around 1880 in official accounts, removed the hard shell. The seeds can therefore be milled without peeling. Then come mash with water and salt, roasting and pressing. Whole dry seeds are not roasted and then pressed.
Origin