Why does Bloodthirst attack multiple targets?

I’m trying to get the achievement “The Steel Has Been Bought”, but the instant I hit Ka’graz with Bloodthirst it killed Aknor simply because he was standing nearby.

There is nothing in the tooltip for Bloodthirst, and no talents that I have, which imply that it’s supposed to hit anything but its primary target. What’s going on?

Do you have any stacks of the Whirlwind buff?

D’oh, that must have been it.

I eventually got the cheesement by taking down Ka’graz entirely with autoattack. These attacks didn’t consume the whirlwind buff, and left Aknor alive. Yay, new Draenor follower!