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Based on the icon, it looks like the Nord racial 2H passive, however. Since it was a 2 hour buff, it could be anything from XP Scrolls, purple food buff, etc.
I've always thought it was a quest achievement buff.
I can say it's not related to being a Nord (I'm not), and I've never used an XP scroll.
I play a nord and don't have that listed in my active buffs, so it's definitely not that. As for Xp Scrolls, I never really bothered to look at the icons, but I don't 100% believe that's what it is. I'm thinking you're right and it was a result of some sort of quest or something to that effect. I've looked through all the skill passives and nothing has that icone outside of the Nord passive.