Fallout was not an issue here. Fallout comes from dust kicked up from the ground. An airblast well above the surface of the ground will have virtually no fallout. Just the material that comprised the missle and whatever dust that was already naturally floating in the air.
The fallout is material contaminated with the reaction products and unreacted uranium from the explosion. In this small airburst, I would suppose that the cloud consisting of the bomb and target material would remain relatively concentrated and settle in a localized area, but the amount of radioactive material should be the same whether or not it is mixed with ground material and dispersed.
Note that the test subjects saw and described this cloud, and surely direct exposure to it would have been highly dangerous.