Yes he may not be in our world but I think Mr. Gold believes he is in our world.
He’s spent possibly hundreds of years creating the curse to get back to his son, so although something could have happened that would have sent Bae to a different land, I think Mr. Gold truly believes he is in the same place and same time as his son.
Not to say that makes my theory right. I’ve been way off before. The show keeps surprising me and I like it that way. 😀