My guess is Jean was sitting with his ice cream on the couch. He has his earbuds in, listening to whatever (the tv in the crime scene video showed a JFK show I think), and he sees the light start coming in the door. At this point, Guyger has tried the lock (which Jean didn't hear because of the earbuds) and is pushing the door open, noticing it's ajar. She pulls her gun as she opens the door, she sees Jean in the living room (the tv and laptop both had light that would cause her to look in his direction immediately (I'm not positive here, laptop could have been in "sleep" mode and dark but the family said he played fantasy. He could have been checking his team)). By this time he's put his ice cream down and pushes himself forward as he starts to stand up. She shoots, hits him and causes him to stagger and take a step forward, which results in her missing the second shot. He crouches as he collapses, sliding backwards at the same time.
The issues I have, start with that there was a light directly over Jean's door. As she opened the door there's no reason the light wouldn't have lit the big mess from behind her, forward. There's also a red stand, no endtable with bright flowers and a few other things in the background. She's 5'2" and the light was up top. It would have filled his apartment in front of her, that's basic lighting. No matter what happened before... this specific point should have made her stop and take inventory. She would have light shining on at least 30% of the room and Jean was a straight up slob.
The prosector should continue to downplay how she got to the wrong place and play up her actions once at the door big time.
I ESPECIALLY liked the repeated times the prosecutor pointed out she had a taser and pepper spray.