Hi.
Myths and legends loosely based on historical accounts are common place.
Robin Hood
King Arthur and the knights of the Round table
So too could be bible stories, to include Genesis.
If one picks and chooses which stories they believe to be factual based on their religious beliefs rather than evidence, then are they not operating in a confirmation bias?
If someone also picks and chooses which elements of a particular story is fiction and which is not, based on whether it is easily defensible, then again confirmation bias is the result.
"You were not there for the beginning. You will not be there for the end. Your knowledge of what is going on can only be superficial and relative" William S. Burroughs