It was shot on film so they had a lot to work with, even 1080p is still probably not high enough resolution to really capture it (I think 1080 is comparable to 35mm on paper but the silver halide crystals don't fall on an even grid like pixels do, so you'd still need a higher resolution to actually digitize it well.
Kind of like how VHS is nominally well below 480p but you really need a minimum of 720p to actually capture it acceptably.
i never thought i'd live to see 35. my dad used to hand out 'make your own bomb shelter' instructions with the boy scouts, i always wondered why his generation seems less worried about it than i was (am).
This footage is just digitized from film and cleaned up a bit. This is part of Atom Central- the group that did Trinity and Beyond and the other atomic documentaries. They did a bluray release of Trinity and they are slowly digitizing and publishing more clips in HD. Their channel has lots more clips