Maybe Grimm & Co used to sneak back and forth between worlds, collecting stories, and Rumple busted them on one of their trips, and when he found out they came from a land without magic, that’s how he got the idea that Bae had come to our world. And maybe they struck some kinda deal with him where he made them promise to leave his REAL story out of the story they told about him, which is why we never knew the true extent of his power and the significant role he played in all the different tales. Maybe he wanted it that way because he didn’t want our world to know how truly powerful he was, once he got the idea to follow Bae here. And as the story progresses, Rumple and some ancestor of the writers will meet in our world and either work together, or against each other.
The more outlandish this theory gets, the more I like it. LOL 😉