That isn't what Susanoo is saying. He's saying that given the amount of divine power used by Shikon-taku, his "simulation" is in effect the creation of a new REAL world. Remember that these deities and divine objects are multidimensional beings not governed by the usual rules of spacetime. It's already explained at the end of the last chapter that the simulated world Shinshuu Onogoro is an actual reality, created with the demiurgic powers of the Spear of Creation Ame-no-Nuboko, the exact same thing Izanagi used to CREATE OUR WORLD. The bell, in order to prove a point, went full demiurge and created an entire new world complete with its own sentient people for Miyo and Susanoo to play with. It's just that due to the lack of love and worship from the human mantra, the new world could only ever be a limited simulation instead of the real real thing.I didn't miss it. It's a sandbox that simulates the way humans work. They are virtual entities built to mimic the way gods think humans behave. They are just puppets
Also, it's hinted that the bell is either Izanagi or is currently being animated by the power of Izanagi. That's what Susanoo probably meant when calling it the "geriatric old man". So his act of making the simulation world is exactly the same thing he originally did with our world.