If what we are seeing is the tail end of the rocket (accounting for the bright spiral and all the pretty colors ... oooooooh) and that rocket did, in fact, malfunction then perhaps the expanding dark spot is some sort of smoke expelled by the rockets exhaust, hence we get the dark expanding spot instead of the bright spirally light (I watched the video again ... pretty lightsssss). Probably is exaggerated by eyes playing tricks and going from relative bright to relative dark (possibly further exaggerated by the electronic device as well). Then again maybe it's an evil villain opening a portal to our world from an alternate universe. He should be leading his triumphant army through town at any minute.