Take your pick: which is the most popular misconception? 
The Hindenburg blew up because it was filled with dangerous/flammable/explosive hydrogen. (See 3.4)
The Hindenburg was designed for helium-only, but the Americans would not sell it to the Germans, who then were forced to use the dangerous/flammable/explosive hydrogen over their most vigorous protests. (See 3.1)
The Hindenburg made a tight turn, a wire broke, which cut a gas cell, hydrogen escaped, mixed with air, then the mix made a u-turn at the covering, then resisted dispersal and diffusion until the nose ropes grounded, which generated a spark at the other end, which got under the cover near the oxy-hydrogen there, which caught fire, and that ignited the covering. (See 3.5)
Or maybe it was a stuck valve, since that had happened before. (See 3.2)
Or, just like in the movie, a mad bomber placed an explosive device timed to go off after the passengers disembarked and its firey blast ignited the dangerous/flammable/explosive pure hydrogen in the cells which then also exploded spreading fire to the covering. (See 3.4)
Begin with 3.1. LZ-129 Evolves
Continue reading to 3.2. The US Navy and the Hindenburg
Continue reading to 3.3. Hindenburg Götterdämmerung
Continue reading to 3.4. Hindenburg “Explosion”