If that's the case, then you'd be hard pressed to find any two people in the world who worship the same god...because each worships his own idea of what his god is, and no two are alike. And that would be true even of a pair of Episcopalians sitting next to each other on a pew.
If the deities involved are make-believe and fictional, then the whole question of what "the same god" means becomes kind of meaningless.
It is fairly meaningless. Angels on a pinhead style debate. Everyone's personal idea of what their deity is like is all that counts. It's not like they are thinking about some real being. It's just an idea.