You mention ancient astronaut theorists. Some of them at least believe this was or could have been a nuclear explosion (war of the gods or something similar). You mention pottery shards turning into melted glass, which could only happen at a high temperature. Something similar may have happened at Mohenjo-daro.

Obviously scientists would say that this is beyond the technology of the time. But they would probably dismiss ancient astronaut theory.

Do you have any thoughts, since you haven't mentioned that possibility?