Just because people write fiction about Harry Potter, it doesn't mean Harry Potter isn't real.
Is God's name Yahweh? Vishnu? Or one of the other names given to the Gods of various people? Who God is or who the Gods are varied from culture to culture. But, if the story about "God" are fictional, then what those people believed about their God wasn't true. It was what they made their God into.
But Baha'is cannot agree with any Hindu sect that has multiple Gods. They cannot agree with Trinitarian Christians. So lots of people believe in concepts of a God that, according to Baha'is, is false. So it's not just the stories about God were fictional. The God in those stories isn't real. But, of course, their invisible, unknowable, unprovable God is real. And why is that? Because Baha'u'llah had something about him... That special thing. He was a nice guy. So whatever he said must be true. And besides, he was a prolific and fast writer and dictate like nobody's business. And he said there is a God and told us what God is like... He's grand and great and way beyond our comprehension. But also we can know him by his attributes... He is all loving, just, kind, and all that good stuff. But created a world filled with pain and suffering and put us here, and, if we screw up, he says he's gong to judge us and we'll have to pay a price.
Invisible God? Pay a price for doing wrong? Sounds like something a parent would say to their kids to get them to obey even when they weren't around. How did that song go... "He knows when you've been good. He knows when you've been bad. So be good for goodness sake." That wasn't real, but it worked... 'til the kids got older. But the invisible God thing still works on a lot of people. Do religious people do "nice" all the time? No. But maybe they're being better than if they didn't believe. But some of them are pretty nice and try and show "God's" love to others. Ah, but they get to look forward to being rewarded when they die. So what's the big deal if they believe or not?
Unfortunately, some religious people take it too an extreme. They'll even kill for their God. Other religious people kill themselves for God. How real is that? Killing and dying for an invisible God that they can't prove is real. Yeah, it's best we check and recheck and make sure what religious people say is for real. If they can't prove it, and believe it anyway, then there's always going to be those that take their beliefs too far.