From Legonia

In the religion of Peng Cheng, the Peng is a giant mythological bird creature made by the big Something. The Peng should have placed the island of Peng Cheng into the ocean and gave it its name.

Peng in other cultures

It's a possible theory that the peng myth maybe is based on a giant Goru species that seems to be died out. In this case, the Peng Cheng- bird is identical with the mother of all Gorus worshipped by Tsinka legends.

Other mythological and immortal birds appear in the Ystel mythology. So not only the big Something, but also the god Nukte could have been the creator of the peng.