I don't use Reaper video editor, and I haven't had time to check my theory but ...
There's a "blend mode" used in video/image compositing (the interweaving of pixel layers) called "Subtract". Justin's video is called "Subtraction" so I'm guessing that he used a Subtract mode to blend the layers - possibly in order to get the cymbals to appear in front of the Acoustic Guitar Player. (also, using Subtract maybe then led to the unintended effect of the background layer bleeding through the Bass and Lead Gtr players).
He also must have used a Crop or Mask on the left side of the screen, as you can see the Ac Guitar Player disappear while walking off.
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