In all likelihood, 'big bang ghost stories' are fictional. Although we might hear some really spooky tales associated with big explosions, these are likely just the result of our natural inclination to create stories to make sense of the chaos and destruction caused by such events. We love to add an element of the supernatural to extraordinary events, but there's no basis to claim they are real.
I think they are mainly fictional. While a big bang can be a very traumatic and shocking event, the idea of ghosts appearing because of it is more of a superstition. For example, in many cases, people might be in a state of shock after a big explosion and misinterpret normal things as ghostly apparitions. There's no scientific evidence to prove that these 'big bang ghost stories' are real.
Most 'big bang ghost stories' are fictional. They are often created by people's overactive imaginations after experiencing or hearing about a big and sudden event like an explosion.