First and foremost, EMP. The EMP blast from a nuclear explosion would have prevented any video of the blast being recorded. While a 1 kiloton blast wouldn't have leveled the area flat like Hiroshima or Nagasaki, the EMP from it would have traveled upward of 20 miles away from the blast. Knocking any and all cameras out LONG before the actual light of the blast would have been seen.

Second reason: There were debris and containers around the crater. Again, if we're talking nuclear, the flimsy (relatively speaking) materials that containers are made of would have meant they would have been vaporized by the detonation. Yet within only 20 feet or so of the crater, you have over turned trucks and trailers.

Third: No reports of mass blindness. The light from an atomic bomb is VERY bright. Enough that if you look at the explosion without protective visors, you will go blind. It burns your retinas out in an instant. Yet there are reports of people in the nearby buildings who saw a fire, followed by a blast. Those people are still able to see, thus their eyes weren't burned out.

Do you want me to continue?