The fast falling dirt would work the same way in a vacuum chamber.

But I dont think of hoax. Its just a typical conspiracy pick-the-parts-we-like documentary.
The radiation would not have been enough to cause direct harm.

Also: only the gamma-rays could have had any effect. Alpha and beta
rays where shielded for easily. (just saw a show about
nuclear plant workers, and they where entering conterminated areas
with higher radiation counts than the astronauts, in much
thinner suits)

The other parts is just about the russian mission.
Of course they used some filmsamples in an uneven order.
Noone would have allowed the filmcamera (cockpitshots) inside
the craft right before that important launch. (Gagarin)
They had better things to do. So they just used a testshot before the mission - no point to complain really, proves just
that propaganda films try to have a nice flow.