It says, "the fireball...is three times hotter than the surface of the sun". Won't you get toasted from only 7 miles afar? Or, maybe the fireball is ephemeral so the heat the fireball produced doesn't do damage?
Meaning that at 20m from the center of the explosion (the fireball was 20m diameter, or 10m radius) it should already be at 1/4 the intensity, already less than the surface of the sun. At 7 miles or 11200m, you're talking 1/(1120^2) or 7.97e-7 of the original intensity - effectively zero - if I've done that math right.
The energy is going in every direction, not just at you. With distance, you will receive a smaller portion of whatever energy made it 7 miles out.
The interior of the sun however is a different story (around 1.57*10E7 K per Wikipedia)
This is a phenomenon of some interest, since it intuitively seems like the 2nd law of thermodynamics should prevent this from happening: http://en.wikipedia.org/wiki/Corona#Coronal_heating_problem
how i understand it is two-fold. first, heat density. the surface area of the explosion is significantly smaller than the sun, and so the energy in the explosion is condensed to a smaller area and thus creates a higher temperature. as it expands it will, therefore, "cool" (relatively speaking) and by the time it reaches 7 miles away it wont melt the piss out of the camera (it obviously survived).
second is the spread of heat from the explosion to the camera. heat transfer is not instantaneous, and so the camera was just fine at this point. again, by the time it spreads to the camera it's dissipated so much energy that the heat will be relatively cooler.
finally i imagine the camera was pretty well protected to withstand the various forces of the explosion.
[1] http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html
EDIT: If it was 3 times hotter than the centre of the Sun...yeah, the Earth might be done for at that point.