The "beach camera" pictures, I spent some time looking at google maps, the Imray nautical charts etc and I am fairly confident that the low green light shown on the video is at the end of the harbour wall on the Sochi Yacht Club, it is the only likely candidate. If you plot a line roughly looking up the beach at the angle shown in the video, then the light that appears in the sky briefly is in the correct alignment for the light on the harbour wall at the Port Of Sochi, which is elevated on a tower. The shape of the light and the distinct on/off is consistent with a nautical light rather than an explosion.