A few things.

ICs are a lot more sensitive to EMP than vacuum-tube devices.

The amount of EMP experienced is a function both of the size of the size of the nuke, and of the receiving antenna. One reason the Starfish and Hardtack bursts affected street lighting systems is that these were attached directly to the electrical grid: power lines == large antennas.

Blast yields were also in the megaton range, 1000x greater than the one here.

https://en.wikipedia.org/wiki/High_altitude_nuclear_explosio...

There were no "sensitive electronics" in 1957. There were pretty much no electronics at all, particularly not in cameras. The transistor was just invented.

Vacuum tubes hold up better than today's little transistors, and there are ways of EMP-protecting things, like putting them in Faraday cages.

Fairy nuff, I thought transistors might have been used in 1957 but I guess not.

The nuke was pretty low energy and it didn't go off in the ionosphere, so no.

Wouldn't they have used a mechanical film camera? I don't believe that would be susceptible.