Correct, critical crafting is what gives you the augment slot.
Reverse engineering a tier 1 purple into a tier 2 purple gives you a recipe that has extra ability modifications, not an augment slot.
If you then manage to critically craft from that item, you then get the augment slot as well and the [superior] tag changes to [Mastercraft].
As for looted items of any color providing recipes, we just don't know yet, which tends to imply that no recipes will be forthcoming from doing so, only meager materials.