Goda planned it all, like Hita Hita no Mi, lol
What people fail to realize is that Oda has planned a lot of things in the story, that he wanted to reveal at specific points in his initial vision for One Piece, that was only supposed to last 5 years, which was supposed to be Luffy's Journey to beat the Four Emperors, and become Pirate King. The problem is, is that the story kept getting longer and longer. We have no clue what was originally supposed to happen, and what's new. And things that Oda planned so long ago, only coming to light now is bound to happen, because 80 percent of the middle of the story was added along the way.
What I do find funny though, is that the references to Nika dating back all the way to Skypiea, is being brushed off like it's nothing. Like Oda was just flipping through One Piece one day and saw that he said some random thing about some random God back on Skypiea, and went, "Fuck it, I'll turn that into Luffy's real Devil Fruit." Seems legit...