Something similar happend to me last night. I was just on the way towards undercity. 80 DK and 49 Shaman x3. That mage was mounted on the gate to undercity and seemed like he was afk.
I targeted him and he just ran towards me, dismounted and casted something (prepare for fight). As he was 64 and could see my group, why the hell did he even think he could kill me?
One lonely Mage at 64 against a fully geared 80ish DK?
My server is a pve-server. That dude was just pvp-flagged and way too low for me.