A shock wave travels at the speed of sound, by definition. I suppose some kind of blast front could go faster, but I think it would be extremely destructive in that case. I’m thinking they were a lot closer than they should have been.
The blast wave, depending on the size of the blast, can travel much faster then the speed of sound. And this was one big blast. I’d said about the size of a tactical nuke, 1 or 2 kilotons, so I think it is a safe bet that the blast wave exceeded the speed of sound.
Also, some phones have poor synchronization between the image and the sound recording.