Ancient Nord Armor (also know as Draugr Armor) has some wierd interactions with smithing and heavy armor perks.

1. (most known) Ancient Nord Armor tempering is affected by the "Daedric Smithing" perk.

2. Ancient Nord Armor and "Matching Set heavy armor" perk.
Any Combination of Ancient Nord Armor and Daedric Armor can trigger the bonus of Matching Set.

3. Ancient Nord Gauntlets and "Fist of Steel" perk.
Ancient Nord Gauntlets have a base armor rating of 10 but give a bonus 18 to unarmed if you take the perk.
(The perk does not check the base armor rating. It cecks the "material".)

The CK shows that all Ancient Nord Armor parts are listed as "Deadric material".
Smithing, Matching Set and Fist of Steel believe that Ancient Nord Armor is Deadric.