I don't see the inches there, the overtake was pretty good imo (look at the front view) and the distance from the rear was okay - it was a bit closer prior to the overtake, but that is normal behaviour.
Except for the "pistol" hand sign, I don't see a problem. Even then, I don't see it as being malicious.
I think you need to understand the effect on distance the wide angle lenses on these cameras have. It's the old 'objects in the rear view mirror may be closer than they appear' disclaimer on convex rear view mirrors - things can seem further away over a designed distance, then suddenly seem to get very close.
From my experience looking at such footage, I'd gauge the driver was no more than 2 feet from his rear wheel, potentially less.