How is possible to alli get of me of my mount?

Hello,
How is possible to alli get of me of my mount?
I did somes pictures,and we can see for a moment dk become horde, How is possible?
It's a dk and a pala, normally they can do fear or control so idk,

Can i report?

There's nothing to report here.
Check combat log next time, perhaps they've used some sort of item or something.