Huh, I thought it was kinda weird that my Norfleet was explosive, but I never really thought anything of it. A friend of mine duped it for me a while back. Taking a closer look, it even says it does bonus elemental damage, which seems kinda weird considering its explosive nature.
Explosive norfleets are modded, bottomline. Hyperion etech pistols can spawn without an elemental dealing explosive damage. Doc mercy quest item is the only other etech that can spawn non-elemental doing non-elemental damage. Gearbox confirmed this as a mistake on their part.