Learning Khaz Algar Skinning from skinning the 'Sewer Beast' Rare in Stormwind!?

I was on my hunter Rhaen in Stormwind, doing a Cooking Daily Quest in the canals, when I saw a night elf druid player getting walloped by a Rare-type creature–the ‘Sewer Beast’ that spawns in the Stormwind Canals. It killed the druid, and because I was floating in the spot in the water where it normally spawns, it started to attack me. My pet and I narrowly survived the encounter, narrowly killing the rare, and when I skinned it (Rhaen is a Skinner/Leatherworker), it automatically taught Khaz Algar Skinning. And my hunter hasn’t even started any ‘The War Within’ content yet!
Is this a bug?