MTG AER: Tezzeret's Touch and Audacious Infiltrator artifact interaction
'Artifact Creature' is not a thing by itself, it is two separate things. What it means is 'this permanent/card/spell is an Artifact' and 'this permanent/card/spell is a Creature'. Since the permanent is both a Creature and an Artifact it is effected by things that effect Artifact Creatures.


  205.2b Some objects have more than one card type (for example, an artifact creature). Such objects satisfy the criteria for any effect that applies to any of their card types.