These two guys thought that it was the smoke that helped their balloon to rise. So, they initially filled the balloon with dense smoke. Then they realized that what was rising the hot air balloon was the hot air.
An interesting fact: The first public flight of a hot air balloon was in 1783, in Annonay, France. That balloon rose to a height of 1,000 meters, and went up in the air about 2 km.
The first hot air balloon has been destroyed when landing by some local peasants because it was flying over and landed in their fields.