Hi,
Here at least, dried figs are now common in lots of shops.
If such a fig is thrown in the wild, birds will peck at it. They will poop it where they will, and often near their nests.
Some birds do nest in small cavities and some seeds will sprout in those cavities.
I'm in Zone7, and this year, I found a figtree growing in a wall of an old Vauban fortress ( Vauban was an engineer in the XVIIIth century).
The tree is something like 5 years old. For now no fruits on it.
The problem with seedlings is finding one that fruits edible wares.
Since yours has fruits ... I still think that it was planted there or nearby before sprouting there.