Well, the Chinese nuke test videos are fake af, especially given they ride horses I to the explosion and send firefighters to roll out hoses. The "computers" involved are also fake af. The original US test footage was edited together by the same fellow who edited the Zapruder footage of the JFK assassination and slow motion is a key element of editing used to make the explosions seem larger than life. I've also heard it told that two bomb tests were set up for these videos. In order to compare the size of the explosions, they stacked one side with TNT and, a few miles away, was "the bomb." Only... both sides had TNT and each side was told the other explosion was the nuke. Unsurprisingly, the explosions were the same exact size. As for what it takes to make a giant mushroom cloud, it definitely does not require a nuke. Thermobaric explosions, where the air is heated in a smaller or series of smaller explosions, prior to the detonation of the main payload will make very pronounced mushroom clouds. Short of running over to the sites of the explosions with a Geiger counter, there wouldn't be much to tell the difference. Consider that Hiroshima and Nagasaki aren't nuclear wastelands, as well. There was no nuclear winter, there. They rebuilt immediately.