Here's what I wrote to the reporter who asked me about it (I was only asked whether it was legitimate, new, revealing, etc.):

Some of that footage had been released previously, but what was available publicly was bits and pieces at less resolution. Having the full, apparently unedited (?) footage is a nice addition. It appears to be the sort of footage that in the US would be intended for policymakers — not-too-detailed, not-too-technical discussion, carefully avoiding certain views (despite appearing to show the innards of the bomb, they carefully avoid the very sensitive bits), but more than the general public would get.

It all appears genuine to me and meshes well with what we already know about the testing. It’s interesting that they’ve released it, though I would not probably read too much into the timing of it (if their bureaucracy is anything like our bureaucracy, the release of old film footage is not actually something that is coordinated at a high level).

In terms of the official US reaction, it was mixed. The public reaction was as the article made clear — "ho hum, making big bombs is easy, this doesn't change anything, and smaller, more-deliverable bombs were the real technological sophistication," etc. They condemned the testing, along with most of the world, as a bald disregard to peace, and a terrible contribution to global fallout (though it was much "cleaner" as a weapon than they initially realized). It made for easy propaganda on the US's part, though interestingly the policymakers were aware that if they condemned it too much, their arguments could be used against US testing as well.

At the same time, behind the scenes and swathed in secrecy, the military did ask the Atomic Energy Commission to look into what it would take to build their own 100 Megaton bombs, in case they wanted to do so. The AEC thought this was stupid — basically, they felt that the US military only wanted them because the Soviets had them, not because they had any real utility — but they did do some work into estimating what this would require (they thought they could make a much more sophisticated weapon than the Soviets had made, but it would still be huge — there is only so much you can do to reduce the weight on weapons with that much fuel in them). They got as far as preparing to test some drop shapes (the massive bomb casings) but the Kennedy administration decided it didn't want the adverse publicity that would come if wind of that got out, and had them drop the issue. The fact that the Soviets had tested several bombs of "very-high yield" (as the US designated these tens-of-megaton monsters) and the US had not (nothing larger than the 15 megaton Castle Bravo test, and that was an accident), played a role in the discussions about ratifying the Limited Test Ban Treaty, which would ban atmospheric tests. McNamara testified that while the Soviets probably did know a bit more about "very-high yield" weapon effects than the US did, this was not really germane to the present or foreseeable US nuclear posture, which would rely on smaller, more deliverable warheads, which the US could test underground.

There were some in the military-industrial complex, the Edward Tellers of the world (including Edward Teller himself) who maintained that this was a gross concession, and the compromise under LBJ was that if the Soviets violated the LTBT, the US would be prepared to test "very-high yield" weapons in outer space on a very short notice. This program was maintained through the mid-to-late 1960s, when it was finally discontinued and it was clear that even the Soviets were not pursuing these weapons.

The US, as an aside, had contemplated 100 megaton bombs as early as 1944. Teller had himself contemplated designs in the 1,000 to 10,000 megaton range. A proposed 60 Mt bomb design had prompted Eisenhower to ban the labs from working on high-yield weapons without permission from the President. There is a longer history to these kinds of "mega bombs," one that I hope to be able to write someday! These "very-high yield" weapons are a research interest of mine, but there is still a lot of work to be done (this is a far-far future plan). Much of it is still steeped in heavy classification, however (the last FOIA document I got on the 1,000 megaton design work had literally every single word redacted except for the titles and dates). So it may be some time! I have written a bit about these things here, some time back.