Terror

[internetdotcom]

Your question has already been answered on the AB.

You must have been using a shadow.  Shadows get random equipment.  Random equipment might include a "hit causes monster to flee" affix.

Yeah, I just thought of that actually. That could be it, but it also happened when I hit a monster (to that monster) and my shadow was off fighting another monster. Could it be an aura effect where we would both get it within range? If so, there was no visual effect.