Not a folk tale, just a visible representation of the local competitive environment. Animals in the Galapagos are generally less flighty because the entire ecosystem is not very competitive: everyone lives off the bounty of the sea. The booby birds, the iguanas, the tortoises... are not intimidated by us because there are no land or air predators to eat them -- not in their risk profiles. Like any other security measure, you optimize for the challenges you expect.

In other environments, apex predators still have a flight response because they still have predatory competition (e.g., wolves against other wolves, or other dangerous situations). The flight response increases based on individual vulnerability - e.g., a well-fed pride of lions will barely observe nearby vehicles on safari (they are some of the most self-confident animals you may encounter) but hungrier singles take more notice.