It’s just a theory but I think Byakuya reboot promotion clip revealed to us that first Medusa was also dropped from the moon and it wasn't explosion already on Earth. Whyman was already on the moon when first petrification happened. Maybe also he doesn't know how to avoid it when it's coming at you. It’s possible that Senku is first person who found way to avoid petrification when it’s coming at him.
I checked and Shamil and others didn’t see moment of Medusa dropping on Earth. They noticed already happening explosion. That’s why we were wondering if it was explosion on Earth or something dropped on Earth. Looks like first petrification weapon also dropped from the moon.
Link to the clip:
https://www.youtube.com/watch?v=T5rUyPVHU-I










