The video angle published by the BBC is better, it appears to show one side of the rocket disintegrating and sliding down non-explosively before the large explosion really kicked in. Would hate for this all to be described by a few missing bolts

https://www.bbc.co.uk/news/videos/cvgz0pdg32mo

edit: the failure appears to start at the bottom, this seems to have damaged the structure enough to cause the sliding to start, then the huge fireball seems to begin with a small flash closer to the top of the rocket