im not sure but that looks liks you didnt put him into final stand. if you look more closely, you will see right before you knife that there are bullets hitting the ground a little ways away behind the enemy to the right.

if i am correct, that means while your teammate shot him and as he was going into final stand, the enemy got the all infamous "invincibility" time that one gets while dropping into final stand which in turn is why you got the hitmarker.

im shore it wasent a hit marker it was because he had final stand on soo he went on to final stand and killed you .