In fact, the entire point of this test was to demonstrate that it was safe to stand under it. While some of the early tests were very unsafe, by the time of this test (1957), the dangers of radiation were well-known, so it wasn't a cowboy-type experiment like the early ones, and the planning would've computed the expected radiation dose and ensured it was safe.
The military did it as a publicity stunt to assuage public fears of nuclear-tipped air-to-air missiles by showing that even if they were used in a dogfight directly over a city, they wouldn't pose any risk to those on the ground. The volunteers were even supposed to not wear a helmet or hat to show that it was fine for normal people. If I recall correctly from having seen this discussed previously, they measured radiation doses received, and found that the highest doses (but still not at dangerous levels) were received by the pilots involved in the test, not the ground volunteers.
This was from the relatively short-lived era when several militaries were hoping to make a distinction between "strategic" nuclear weapons, the kind that blow up cities and would only be used in doomsday scenarios, and "tactical" nuclear weapons (http://en.wikipedia.org/wiki/Tactical_nuclear_weapon), small-yield varieties that would just be like very big regular weapons and could conceivably be used in a non-apocalyptic war. Due to a mixture of public opposition and fears of international chain reactions that might result from "going nuclear", though, that initiative failed, which is why you saw a transition back into really-gigantic conventional weapons in the 1990s, e.g. the MOAB (http://en.wikipedia.org/wiki/GBU-43/B_Massive_Ordnance_Air_B...).
