I know the PS4 doesn't actually record when the trophy pops but I did receive it after I killed the last guy in this video. I also obtained the platinum. TIPS: If you're using Axii, you should approach on their right and then aim the crossbow at their head and fire. When I was on the left and sometimes behind them, it would miss completely even though the reticules were directly pointed at the enemy's head.

THIS IS THE MOST FRUSTRATING TROPHY I HAVE EVER GOTTEN!