I am pretty sure it is part of the video compression that works on the basis of what is in the foreground and what is in the back ground. Foreground
stuff stays sharp and in focus but background stuff goes pixilated to the point of being blocky. Since he was in a pretty dark setting everything
else is seen as pretty much flat and so maintains a constant level of resolution. His face, however, is well lit and the 'highs and lows' of his
features are more important. This coupled with a bad bit of compression is what I think is causing the patterning.
He is probably out without a crew (a one man shoot with the camera on a tripod) and the camera is setting its own depth of field etc as the story
progresses so the effect transitions in.
my $0.02


