An off-hand attack (as per TWFing) is not the same as an attack with the off hand. The off hand is the non-dominant hand. It's confusing terminology, and most likely, the glossary entry is a remnant from 3.0, but since it's there, we can't just ignore it while discussing RAW; chirality is still a thing. Off hand is defined in the rules (unless you want to claim the glossary isn't part of the rules).
Attacking with armor spikes (or any other weapon that isn't wielded in the hand) has nothing to do with handedness.