Anecdote: Last night a dragon engaged me, I started casting a firebolt, then a giant and a mammouth started running at me.... passed right beside me, attacked the dragon and killed him... WTH, my kill! I killed em both to feel like I was not too opportunistic!
I had a similar thing to this happen to me the other night. I'm using a bow to try and hit the dragon. So I'm spinning in circles with my view skyward trying to follow the rotten thing. And I see the "tremor" on the screen. So now I'm thinking the dragon landed. Oh no... that'd be the mammoth and his giant friend rampaging in my general direction. I was not so fortunate as to have the new guys focused on the BIG DRAGON IN THE SKY. Nope, they wanted lil' ol' me. Pfft.