This was a tactical nuke. I don’t know if it was one of the lost suitcase bombs missing from Russia years ago, or a highwire tactical nuke recovered or stolen during a covert military operation, or even a contingency nuke acquired from one of the nuclear member nations. Anyone who has planned to use these weapons in the past, though never employed, knows what these weapons can do and what their signature is and what this type of weapon envelope looks like. I’m saying it now. I don’t care what the consensus is for public consumption, this was a small tactical nuclear bomb.
A groundburst nuke would have produced a blinding flash. No flash. There would also be all kinds of radiation signatures that any university-level physics department or nation in the region could detect.