What exactly cons utes an explosion? What you simple-mindedly refer to as an "explosive" is only one of many things that can cause an explosion, and many more things can create an explosive sound. If a plane hits the side of a building, that's an explosion. If the fire blows the doors off the elevators at the bottom floor of the building, that's an explosion, if load bearing members suddenly fail, that's an explosion. If tempered glass windows are stressed to the breaking point, they explode. An overloaded generator can explode, as can anything with any potential energy in it, whether it's chemical, mechanical, electrical, or gravitational.
By the way, isn't this guy's testimony about the time the building was hit by the plane and NOT when the building collapsed? Why would they be setting off demolition explosives an hour beforehand?