"Sound" is due to something moving slower than, well, the speed of sound. "Shock waves" travel faster than that.
Really Big explosions can create shock waves that move faster than sound for a long way, but your firecracker examples are just the usual form of sound-based noise.
The sound of the explosion is propagated by the motion of the atoms due to their thermal energy. One way to see this: Far from the firecracker, the energy of the explosion has not increased the energy of the air molecules at all: their mechanism for transporting sound energy isn't about the firecracker at all.
To put it another way: The energy of the firecracker is tiny compared to the energy of the air molecules. A cubic meter of room-temperature air is about 1 kg of molecules, each with thermal velocity of 460 m/s. That's about 100kJ of energy. The fire cracker is much, much less than that, and the sound is spread over much, much more than that.