Regardless of mythological origin or not, the naming and deification of the world speak to the tendency of humans to anthropomorphize and name something the are connected to.
Anthropologically speaking, most cultures see the earth as something alive and to be respected. Tribal cultures do this directly while pagan religions attributed the world or earth to a god or goddess.
Regardless of the reason or understanding of the planetary system, people named the concept of world they inhabited. How They did so was unique to the culture and age they lived in. And it makes sense that a culture that placed so much emphasis and acknowledgement on the planet being a living and conscious entity, such as the Cetra, would have a name to connect to the planet they're speaking with.
Also, while Minerva is the name of the Goddess who represents the will of the Lifestream in CC, we have no idea if that's her only name, her only form, or if there are other personifications or versions of her that reperesent the same concept.
Bahamut is a summon beast yet there are at least 6 separate incarnations of him born from the planet. Whether these represent alternate evolutions or stages of its growth are unknown, but seeing as how Minerva is akin to a summon creature born from the entire planet, it wouldn't be surprising if it went by other names or changed based on the flow and composition of the Lifestream.