I don’t want to be disrespectful, but the video is too short to know what has happened. First, when you got to the enemy, he was already dead. You killed him again, but you didn’t check the stairs.
Second, if you pay attention is easy to see the “revive animation”, and the player starts with 20% of health. It could be possible that he get revived by a medic on the uncheck stairs. And finally, five seconds of gameplay is not enough to see anything at all.