> Why would you run like hell away from your tent without your boots in the Ural mountains night?
-Because you are sound asleep one moment, only to find yourself in the midst of a number of explosions the next? That would unsettle me no end, for sure.
Not saying that I know for sure what happened; only that the simplest explanations often are the best.
I do find it rather unlikely that Soviet armed forces (if they were testing something suffiently secret to 'justify' killing any accidental spectator, even their own citizens) would even let people enter the area; much easier (and less drastic!) to just tell people to turn around 'for security reasons' and be done with it than letting them get too close, then killing them.
Now, death by negligence/indifference in the course of military action, on the other hand, would hardly be a first.
(And if someone WANTED them dead, the area does appear to lend itself well to making people disappear; doubly so when under a regime which had taught people not to ask too many awkward questions.)
It would be rather surprising if anyone but Soviet authorities of one variety or the other was involved in activities which couldn't be allowed to come to light in the area, so I (perhaps too lightly) discount options like a secret CIA infiltration mission, yetis, aliens, poachers, rum runners...)